Early Career Conference in Trapped Ions (ECCTI) 2024

7 Jul 2024, 17:30 → 12 Jul 2024, 19:00 Europe/Vienna

Hörsaal B (Technik) (Viktor-Franz-Hess Haus)

ECCTI Mail, Elise Wursten (RIKEN), Fabian Anmasser, Manuel John, Silke Auchter (Infineon Technologies Austria AG), Simon Lechner (CERN), Tommaso Faorlin (Universität Innsbruck)

 

Join us at ECCTI from the 7th-12th of July 2024!

ECCTI is intended to connect a broad community with very diverse scientific goals with common technical challenges.

We invite graduate students and early career researchers (within 5 years of completing a PhD) to share their cutting-edge work with a global audience. Dive into the physics research of today with a focus on:

• Atomic Clocks
• Quantum Information & Computation, Quantum Simulation, Quantum Technologies
• Antimatter Physics
• Precision & Molecular Spectroscopy
• Nuclear Physics

Why Attend? Engage in fruitful discussions shaping the future of physics. Connect with potential colleagues, broaden your perspectives, and partake in interactive sessions to develop skills essential for a successful career in research or industry. In addition, we will have the honor to host David Wineland throughout the conference, Nobel prize laureate who received the prize for his pioneering work on ground state cooling of trapped ions and for opening the door to the experimental study of the interaction between light and matter.

🌈 We encourage applications from a diverse community. Additional support is available for those facing attendance barriers. Part-time PhD students and those having been on career breaks are exempt from the 5-year post-PhD limit. Each application is assessed individually.

 

Funded in whole or in part by the Austrian Science Fund (FWF) 10.55776/COE1 and the European Union - NextGenerationEU

 

Conference poster

ECCTI Map

Monday's poster session

Tuesday's poster session

Sunday 7 July

Conference Practicalities: Registration & welcome reception

Welcome_presentation.pdf

Welcome_presentation.pptx

Monday 8 July

Conference Practicalities: Welcome to ECCTI 2024

Welcome_presentation.pdf

Welcome_presentation.pptx

Nuclear Physics

Convener: Dr Simon Lechner (CERN)

1 Precision mass measurement of proton-dripline nucleus $^{22}$Al and implications on suspected halo nature in the ground state

Halo nuclei exist at the extremes of nuclear structure where a isotopes’ mass distribution extends far outside the compact core: a consequence of a weakly bound nucleon(s). The unique properties of these isotopes provide stringent tests for nuclear structure models. These nuclei are positioned on the nuclear driplines, often restricting experimental access due to low production rates or short half-lives. Proton-halo nuclei are further suppressed due to the confining effect of the Coulomb barrier. The Facility for Rare Isotope Beams (FRIB) has extended the reach towards these isotopes, including $^{22}$Al whose halo nature has recently been suggested based on observed isospin-symmetry breaking effects in the sd-shell region [1]. The level scheme found in this work, however, contains significant uncertainties as a result of its unmeasured mass, thus impacting the mirror asymmetry parameter. Precise knowledge of these isotopes’ binding energy, i.e. mass, is paramount due to the role of weak binding in the emergence of the halo structure. The Low Energy Beam Ion Trap (LEBIT) facility at FRIB used Penning trap mass spectrometry to determine a mass excess for the $^{22}$Al ground state of $\text{ME}=18\;093.6(7)$~keV, a factor of thirty improvement in uncertainty to the last measured value [2]. This result agrees well with the predicted binding energy from $\textit{sd}$-shell USD Hamiltonians, which also predicts restricted halo formation due to minimal $1s_{1/2}$ occupation in the proton shell. A particle-plus-rotor model additionally investigates the possibility of enhanced s-wave occupation from the interplay of weak binding. Ultimately, our findings suggest the existence of halo structure in the $^{22}$Al ground state would require strong continuum-induced deformation, similar to the suspected situation for $^{29}$F [3].

This work was conducted with the support of Michigan State University and the National Science Foundation under Grants No. PHY-1102511, PHY-1126282, PHY-2111185, and PHY-2238752. This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics and used resources of the Facility for Rare Isotope Beams (FRIB) Operations, which is a DOE Office of Science User Facility under Award Number DE-SC0023633, and under the FRIB Theory Alliance Award No. DE-SC0013617.

[1] J. Lee, et al., Phys. Rev. Lett. 125, 19 (2020)
[2] M.Z. Sun et al., Chinese Phys. C 48, (2024)
[3] K. Fossez and J. Rotureau, Phys. Rev. C 106, 3 (2022)

Speaker: Mr Scott Campbell (Michigan State University, Facility for Rare Isotope Beams)

240807_ECCTI_Campbell.pdf

2 Towards Measurements of Electroweak Nuclear Properties using Single Molecular Ions in a Penning Trap

We present the development of a novel Penning ion trap for precision spectroscopy of symmetry-violating electroweak properties using single trapped molecular ions [1]. The high magnetic field of the Penning trap can be used to Zeeman shift two molecular states of opposite parity to near degeneracy, enhancing the sensitivity of parity-violating nuclear properties by more than 11 orders of magnitude [2]. Hence, our proposed experimental setup is expected to provide highly sensitive measurements of symmetry violating nuclear properties across the nuclear chart. This contribution will describe the status of a cryogenic Penning trap for performing measurements in SiO+ and TlF+ molecules, as well as discuss future prospects of this technique.

[1] J. Karthein, S. Udrescu, S. Moroch et al. arXiv:2310.11192 (2023)
[2] Altuntas, E. et al. Phys. Rev. Lett. 120, 142501 (2018)

Speaker: Scott Moroch (Massachusetts Institute of Technology)

SMoroch_ECCTI_Talk_2024.pdf

3 Progress of the LMU $^{229m}$Th$^{3+}$ Trapped-Ion Nuclear Clock Project

The $^{229}$Th nucleus assumes a unique role in the nuclear landscape for its low-lying isomeric first excited state $^{229m}$Th with an excitation energy of $8.338 \pm 0.024$ eV [1], accessible with modern VUV-laser systems. A nuclear clock based on this thorium isomer holds promise not only to push the limits of high-precision metrology with a fractional uncertainty expected in the range of $10^{-19}$ [2], but also to contribute to dark matter and other fundamental physics research as a novel quantum sensor.
It will also be able to contribute to the search for theoretically expected temporal fluctuations of fundamental constants like the fine-structure constant $\alpha$ [3].

The cryogenic Paul-trap experiment currently operated at the LMU Munich is primarily designed for long ion-storage times, allowing for the measurement of the still unknown ionic lifetime of the isomer. The lifetime is expected to be several thousands of seconds and its determination is essential for the realization of a nuclear frequency standard. In a second step, the setup will be a platform for VUV-comb spectroscopy of the $^{229}$Th nuclear transition, paving the way towards a first nuclear clock prototype.

In this poster, the building blocks of the experimental setup for trapping and sympathetic laser cooling of $^{229m}$Th$^{3+}$ by $^{88}$Sr$^{+}$ are presented and the status of first measurements, such as trapping, storage, and Doppler-laser cooling of $^{88}$Sr$^{+}$, are discussed.

This work was supported by the European Research Council (ERC)
(Grant agreement No. 856415) and BaCaTec (7-2019-2).

[1] Kraemer, S., Moens, J., Athanasakis-Kaklamanakis, M. et al., Observation of the radiative decay of the 229Th nuclear clock isomer, Nature 617, 706–710 (2023)
[2] C. J. Campbell et al., Single-Ion Nuclear Clock for Metrology at the 19th Decimal Place, Phys. Rev. Lett. 108, 120802 (2012)
[3] E. Peik et al., Nuclear clocks for testing fundamental physics, Quantum Sci. Technol. 6, 034002 (2021)

Speakers: Georg Jakob Holthoff (Ludwig Maximilians Universitat (DE)), Markus Wiesinger (Max Planck Society (DE))

2024_ECCTI_Nuclear_Clock_Talk.pdf

Coffee break

eccti_coffeebreaks.pdf

eccti_coffeebreaks.pptx

Quantum Information & Computing

Convener: Matthias Dietl

4 Quantum Information Processing with Trapped Ion Qudits

In the current stage of its evolution, Quantum Information Processing is
following the precedent set by classical computing and generally encodes information in binary form, thus relying on so-called qubits. For many of the systems used to process this quantum information, this is however a rather artificial constraint, limiting the Hilbert space available for computation and introducing leakage errors that slip through the most common error correction schemes. Going from qubits to qudits, non-binary logical base states, to leverage a larger Hilbert space for computation is therefore one path towards building more powerful and reliable Quantum Information Processors that can be used to solve real-world problems. We use trapped Calcium ions to encode information in higher-dimensional qudits up to d = 7, demonstrate comparable performance to a qubit-based processor and set out to build a new experimental setup dedicated exclusively to QIP with trapped Calcium qudits. This will enable us to carry out multiple-different entanglement gates on qudits, reducing the experimental overhead required when entangling higher-dimensional systems.

Speaker: Peter Tirler (University of Innsbruck, Quantum Optics and Spectroscopy Group)

Qudit Quantum Hardware.pdf

Qudit Quantum Hardware.pptx

Qudit Quantum Hardware.pptx

5 Stimulated Raman 2-qubit logic gates in metastable trapped-ion qubits

A proposed scheme for implementing trapped-ion quantum computing encodes qubits in different types of electronic levels where logic gates can be implemented with low cross-talk, know as the omg architecture [1]. One type of qubit this scheme employs is the metastable (m) qubit, which has not been widely studied. We have implemented m qubits in the D$_{5/2}$ manifold of $^{40}$Ca$^+$ and performed one- and two-qubit stimulated Raman gates, one of the first entangling gates performed in m qubits. We perform these gates using laser beams tuned 44 THz red of the 854 nm D$_{5/2}$ to P$_{3/2}$ transition with increased power using a fiberized injection-locked 976 nm diode laser system. The injection-locked scheme allowed for a three-fold increase in gate speed compared to using a single free-space laser diode setup by increasing the power in each of the two beams from 80 mW to 250 mW. We have measured the spontaneous Raman scattering rate from these beams, and comparing these results to scattering models we have developed that account for effects relevant at large detunings [2], we find that spontaneous Raman scattering error rates at this wavelength can be made low enough that they are no longer a limiting factor in achieving fidelities needed for fault-tolerance.
[1] D. T. C. Allcock et al., Appl. Phys. Lett. 119, 214002 (2021)
[2] I. D. Moore et al., Phys. Rev. A 107, 032413 (2023)

Speaker: Sean Brudney (University of Oregon)

raman_gate_talk_draft4.pptx

6 Snapshotting Quantum Dynamics at Multiple Time Points

Measurement-induced state disturbance is a main challenge in obtaining quantum statistics at multiple time points. We propose a method to extract dynamic information from a quantum system at intermediate time points, namely snapshotting quantum dynamics. In order to do this, we introduce a multi-time quasi-probability distribution (QPD) that correctly recovers probability distributions at respective times and construct a systematic protocol to reconstruct the multi-time QPD from measured data. Our approach can also be applied to extract correlation functions for various time orderings. We provide a proof-of-principle experimental demonstration of the proposed protocol using a dual-species trapped-ion system. We employ 171Yb+ and 138Ba+ ions, respectively, as the system and the ancilla to perform multi-time measurements that consist of repeated initialization and detection of the ancilla state without directly measuring the system state. The two- and three-time QPDs are reconstructed, where the dynamics of the system are faithfully monitored. We also observe negativity and complex values in multi-time QPDs which clearly indicate a contribution of quantum coherence in the dynamics. Our scheme can be applied to any multi-time measurements of a general quantum process to explore the properties of quantum dynamics.

[1] arXiv:2207.06106

Speaker: Pengfei Wang (Beijing Academy of Quantum Information Sciences)

Pengfei Wang(王鹏飞)_Innsbruck.pdf

7 Novel tweezer assisted sub-Doppler cooling of trapped 171Yb+ ion crystal

We propose a new sub-Doppler cooling scheme in trapped ion crystals in Paul traps which utilizes a Sisyphus-like cooling mechanism to simultaneously cool all the motional modes of the crystal.
We use a hollow tweezer, tuned near resonance with the transition from the qubit manifold to a short-lived excited manifold, to generate a state-dependent tweezer potential. This introduces a position dependent quench rate for the qubit states. The cooling scheme is completed by using a microwave field to drive the magnetic dipole transition between the qubit states, creating a Sisyphus-like cooling mechanism which is augmented by the position dependent effective lifetime.

We identify the optimal cooling parameters for one and two-ion crystals exactly, and use a variational ansatz to extract the cooling rate for larger ion crystals. We also show that this cooling scheme is relatively robust against tweezer pointing errors. Furthermore, the scheme allows for the entire crystal to be cooled sympathetically by adressing a single ion with the tweezer, while not destroying the internal qubit state of the other ions.

Speaker: Bas Gerritsen (University of Amsterdam, ITFA)

ECCTI24_tweezercooling_presentation_BG.pptx

8 Scalable all-electronic quantum control of trapped-ion qubits

Building useful quantum computers means making them better as well as bigger. At Oxford Ionics we replace the lasers conventionally used to manipulate ion qubits with electronics integrated directly into trap chips, which allows us to reach very low error rates in a highly scalable architecture.
Our all-electronic architecture combines laser-free gates with local tuning of electric potentials to enable site-selective single- and two-qubit operations in a multi-zone quantum processor. Integrated antennas deliver control fields common to all qubits, while voltages applied to local tuning electrodes adjust the position and motion of ions in each zone, thus enabling local coherent control.

Speaker: Marius Weber (University of Oxford)

5_ECCTI2024 Oxford Ionics.pdf

5_ECCTI2024 Oxford Ionics.pptx

Lunch break

Skill session: Seminar by Nobel-laureate David Wineland

9 Atomic Clocks and Einstein Relativity

Speaker: Dave Wineland (University of Oregon)

Coffee break

eccti_coffeebreaks.pdf

eccti_coffeebreaks.pptx

Poster session

10 Beam-transport simulations for antihydrogen production with the GBAR experiment at CERN

The GBAR (Gravitational Behavior of Antihydrogen at Rest) experiment, located at CERN’s AD/ELENA “Antimatter factory,” aims at measuring the free-fall of antihydrogen atoms to test the Equivalence Principle of General Relativity. Unlike other experiments producing antihydrogen, GBAR uses an in-flight charge-exchange reaction of antiprotons with a cloud of positronium [https://doi.org/10.1140/epjc/s10052-023-12137-y].
Since the reaction cross section is proportional to the positronium density, the production cavity must be made very small. This makes injection of the antiproton beams very challenging since the beam emittance is larger than the geometrical acceptance of the cavity.
Therefore a Penning-Malmberg trap is used to collect and cool antiprotons to reduce the beam emittance. [https://doi.org/10.1088/1748-0221/17/10/T10003].
GBAR uses a fast-switching electrostatic decelerator system that provides antiproton bunches at energies of a few keV, which can be injected into the Penning trap [https://doi.org/10.1016/j.nima.2021.165245]. Using the ion-optics program SIMION, the injection optics are simulated, as well as the transport of the antiprotons to the reaction chamber. Results of these simulations will be presented.
Producing antihydrogen ions opens the possibility of cooling them to micro-Kelvin temperatures by Coulomb coupling with a cloud of trapped ions that are laser cooled.

Speaker: Sarah Geffroy (Université Paris-Saclay (FR))

11 Spectral signatures of vibronic coupling in trapped cold atomic Rydberg systems

Atoms and ions confined with electric and optical fields form the basis of many current quantum simulation and computing platforms. When excited to high-lying Rydberg states, long-ranged dipole interactions emerge which strongly couple the electronic and vibrational degrees of freedom through state-dependent forces. This vibronic coupling and the ensuing hybridization of internal and external degrees of freedom manifest through clear signatures in the many-body spectrum. In this talk, we briefly discuss the recent results in Ref. [1] wherein we consider the case of two trapped Rydberg ions that realize a quantum Rabi model due to the interaction between the relative vibration and Rydberg states. We proceed to demonstrate that this hybridization can be probed by radio frequency spectroscopy and discuss observable spectral signatures at finite temperatures and for larger ion crystals.

[1]. J. W. P. Wilkinson, W. Li, and I. Lesanovsky, Spectral signatures of vibronic coupling in trapped cold atomic Rydberg systems, arXiv:2311.16998 (2023)

Speaker: Dr Joesph William Peter Wilkinson (Universität Tübingen)

12 Towards frequency comb Raman spectroscopy for quantum logic

One of the most attractive quantum computing platforms is that of atomic ions. We aim to investigate an alternative approach that substitutes atomic ions with molecular ions, which allows for the utilization of rotational degrees of freedom for quantum information encoding. However, due to the complex internal structure of molecules, advanced methods are required to manipulate and readout their quantum states. In order to prepare, control, and characterize molecules at the quantum level, we are developing a setup for two-beam frequency comb Raman spectroscopy.

The two-beam frequency comb Raman setup allows precise control over driving rotational transitions in molecular ions. We will drive two-beam frequency comb Raman carrier transitions between the electronic D-levels in Ca$^+$. The same system will be used for driving rotational state transitions in CaH$^+$ and CaOH$^+$. The possibility of directly driving sideband transitions with the frequency comb will also be explored. Driving rotational transitions in molecules, especially sideband transitions, requires higher intensities, necessitating the use of an amplifier. Dispersion in the optical path also decreases Raman efficiency. My project focuses on the amplification and dispersion compensation of the comb light used in this Raman setup.

Speaker: Elyas Mattivi (Universität Innsbruck)

13 Towards large scale quantum computing – a many qubit ion trap at room temperature

Large scale quantum computing is subject to extensive research and the ideal platform for general purpose quantum computers has yet to be found. Trapped ions as qubits excel in terms of gate fidelity and coherence times but so far systems have mostly been limited to only a small number of qubits. Our system is designed to support a linear chain of up to 50 ions which can be individually addressed, providing a versatile platform with many qubits and a high level of control. At the heart of the system is a 3-dimensional ion trap consisting of gold coated laser machined glass. The trap operates in ultra-high vacuum at room temperature. Individual addressing is implemented using a waveguide array. One application of this system is research towards large distance error correction, eventually enabling fault tolerant quantum computation. The high level of control is furthermore advantageous for the simulation of complex Hamiltonians, effectively performing quantum simulation at scale. Lastly, the segmented electrodes of the trap allow splitting of the ion chain into multiple segments for parallel quantum processing.

Speaker: Philip Leindecker

14 A compact He-buffer-gas-cell ion source for delivery of $^{229(m)}$Th$^{3+}$ ions into a cryogenic Paul trap

The $^{229}$Th nucleus has the unique property of a very low-lying isomeric first excited state with an excitation energy of only 8.338(24) eV [1], which is addressable with state-of-the-art VUV frequency comb laser systems. Storage in the isolated environment of a cryogenic ion trap will allow for lifetime measurements of the excited isomeric state (expected in the range of a few 10$^3$ seconds), precise spectroscopy of the nuclear transition, and eventually the creation of the first nuclear clock with an estimated systematical uncertainty approaching 10$^{-19}$ [2].

For loading of $^{229}$Th$^{3+}$ ions into the ion trap, a compact version of the very successful He-buffer-gas-cell ion source used in [3-5] has been designed, built, and commissioned at LMU. The compactness of the setup will allow the installation on the laser table next to the ion trap where $^{229}$Th$^{3+}$ will be trapped and sympathetically cooled by laser-cooled $^{88}$Sr$^+$ ions. The challenging boundary conditions of 32 mbar He in the buffer gas cell and $<10^{-8}$ mbar in the ion trap require several stages of differential pumping, which have been implemented.

In this contribution, we report on the commissioning of the compact He-buffer-gas-cell ion source, including the demonstration of the fulfilment of the differential pumping requirements, and first experiments towards transferring $^{229}$Th$^{3+}$ to and trapping of $^{229}$Th$^{3+}$ in the ion trap. In addition, we report on efforts to integrate an ablation ion source for $^{88}$Sr$^+$ into the ion guide between the buffer gas cell and the ion trap for combined extraction of $^{229}$Th$^{3+}$ and $^{88}$Sr$^+$.

This work was supported by the European Research Council (ERC grant agreement No. 856415) and BaCaTec (7-2019-2).

[1] S. Kraemer et al., Observation of the radiative decay of the $^{229}$Th nuclear clock isomer, Nature 617, 706–710 (2023).
[2] C. Campbell et al., Single-ion nuclear clock for metrology at the 19th decimal place, Phys. Rev. Lett. 108, 120802 (2012).
[3] L. von der Wense et al., Direct detection of the $^{229}$Th nuclear clock transition, Nature 533, 47–51 (2016).
[4] B. Seiferle et al., Lifetime Measurement of the $^{229}$Th Nuclear Isomer, Phys. Rev. Lett. 118, 042501 (2017).
[5] B. Seiferle et al., Energy of the $^{229}$Th nuclear clock transition, Nature 573, 243–246 (2019).

Speakers: Dr Markus Wiesinger (LMU Munich), Georg Holthoff (LMU Munich)

15 Towards a network of 43Ca+ optical clocks for entanglement-enhanced metrology

Over the past few decades, advancements in optical atomic clocks have made it possible to measure time and frequency with unprecedented stability and systematic uncertainty [1,2]. Precision frequency comparisons between macroscopically separated clocks have applications in geodesy [3], probing variations in fundamental constants, and in dark matter searches [4].

Until now, most previous frequency comparisons between different clocks have been done on independent systems, which are limited by the standard quantum limit (SQL). In contrast, a set of entangled atomic clocks can surpass the SQL to reach the Heisenberg limit -- the ultimate precision limit in quantum theory -- wherein a system of $N$ entangled clocks sees an improvement of $\sqrt{N}$ in its stability.

We previously demonstrated this enhancement in a network of two $^{88}$Sr$^+$ clocks [5] on the 674 nm $5S_{1/2} \leftrightarrow 4D_{5/2}$ quadrupole transition using Ramsey spectroscopy, reaching a fractional frequency uncertainty of $10^{-15}$, mainly limited by the short probe duration of 20 ms due magnetic field fluctuations. To reach lower uncertainties, we are setting up the next generation of the experiment wherein we map the remote Sr-Sr entanglement onto two $^{43}$Ca$^+$ ions. The 729 nm $^{43}$Ca$^+$ $\lvert 4S_{1/2}, F=4, m_F=4 \rangle \leftrightarrow \lvert 3D_{5/2}, F=4, m_F=3 \rangle$ optical clock transition is field-insensitive at 4.96 G, enabling probe durations of over 500 ms, which is comparable to the start-of-the-art clocks [1]. This improves the fractional frequency uncertainty on each measurement and thus yields a lower overall instabililty.

We will present progress towards these clock experiments, including the setup of a 729 nm laser system locked to a high finesse cavity, as well as fibre noise cancellation on 20 m of fibre length.

References

[1]. S. M. Brewer et al., Phys. Rev. Lett. 123, 33201 (2019).
[2]. E. Oelker et al., Nat. Photon. 13, 714–719 (2019)
[3]. T. E. Mehlstaubler et al., Rep. Prog. Phys. 81, 064401 (2018).
[4]. M. S. Safronova et al., Rev. Mod. Phys. 90, 025008 (2018).
[5]. B. C. Nichol et al., Nature 609, 689–694 (2022)

Speaker: Ayush Agrawal (University of Oxford)

16 Optical integration with femto-second laser written waveguides

Current ion trap quantum computing systems usually make use of free-space optics to deliver the light to the ions. This practice makes the setups susceptible to drifts and vibrations and limits the number of ions which can be manipulated. For a scalable system it is thus necessary to increasingly integrate optical elements from external components directly into the ion trap. We use femto-second laser pulses to write single-mode and polarization-maintaining waveguides directly into borofloat glass. Unlike other materials used in CMOS technology, borofloat glass is transparent for ultraviolet light required for the manipulation of 40Ca+ ions. Henceforth, a microstructured surface trap was realized featuring two of these waveguides, one for 397nm light and one for 729nm light. In parallel, we build up an integrated cryogenic quantum computing system to enable fast trap testing and to investigate the quality of the light delivery to the ions. The cryogenic experimental setup is designed to contain two separated vacua, one rough vacuum environment enclosing the cold head and a ultra-high vacuum experimental chamber with the ion trap. The design enables to separate the experimental chamber from the cryostat under vacuum and bake it for even better vacuum. For the future we plan to further increase the running time of the cryostat by building an additional experimental chamber to be able to swap the chambers if baking or work on one of them is necessary.

Speaker: Marco Schmauser (Universität Innsbruck)

17 Towards a Novel Fiber Based Cold Atom Source For Trapped-Ion Experiments

In trapped-ion quantum computing, the loading of ions from an oven or an ablation target into a trap releases large numbers of hot atoms into the vacuum chamber, affecting vacuum pressure and depositing on surfaces. Furthermore, the challenge of scalability of quantum computers has led to replacing 4-rod Paul traps by surface traps with a lower depth, making in harder to trap hot ions. The QuantumGuide project aims at offering a simplified and reliable loading of surface ion traps, with an improved vacuum quality. This method relies on a Magneto-Optical Trap (MOT) as a source of cold atoms, and on guiding these atoms through a hollow-core fiber using a dipole trap to help the in-coupling. I present a 3D MOT of $^{40}$Ca atoms followed by the realization of a cold atom beam and other steps towards the realization of a dipole trap in a hollow-core fiber.

Speaker: Jolan Tissier

18 A scalable photon interface for trapped-ion qubit registers

We report on a method to interface the quantum state of each individual trapped-ion qubit in a register with a separate direction-switchable travelling photon. By switching the ion-trap confinement, ions are brought one at a time into the focus of an optical cavity and emit a photon via a cavity-mediated Raman transition. The result is a train of photons, each entangled with a different ion in the string. Experiments are presented for a string of ten ion-qubits, yielding an average ion-photon Bell state fidelity of 92%. The method is directly scalable to larger ion qubit registers and opens up the near-term possibility of quantum networking trapped-ion quantum processors, quantum sensing arrays and atomic clocks.

Speaker: Marco Canteri (University of Innsbruck)

19 High-precision mass measurements on highly charged ions with the PENTATRAP Penning-trap experiment

The PENTATRAP experiment at the Max Planck Institute for Nuclear Physics in Heidelberg is a high-precision Penning-trap mass spectrometer that utilizes a cryogenic environment, a stable magnet, and an image current detection system to determine mass ratios of stable and long-lived highly charged ions with relative uncertainties in the few parts per trillion regime. The data acquired by this state-of-the-art apparatus contributes to different fields of fundamental physics, e.g., fifth force search, neutrino physics, and highly charged ion clocks. In this contribution I will present recent measurements on long lived electronic states, Q values of neutrino physics, and isotope shifts followed by future perspectives of PENTATRAP.

Speaker: Jan Nägele (Max Planck Institute for Nuclear Physics)

20 Quantum technologies with trapped electrons

At the University of Sussex we are developing a novel planar Penning trap technology. We are particularly focused on the applications of trapped electrons in quantum technology, specifically as a quantum microwave transducer. The potential applications span across various domains, including fundamental physics measurements, such as determining the neutrino mass, and technologies such as quantum radar, quantum microwave microscopy, and mass spectrometry. We have coined the expression Geonium Chip for our novel trap in honour of the pioneering work of Dehmelt, who first introduced the concept of 'Geonium' to describe a cloud of electrons confined in static fields. In my talk I will introduce our ion trap and discuss some of the elements that make it a scalable and readily deployable quantum technology. One of the most significant advantages over conventional Penning traps lies in our innovative tuneable planar magnetic field source, capable of producing homogeneous magnetic fields of 0.5 T. This breakthrough marks the initial stride towards obviating the necessity for large, non-scalable, and exceedingly expensive superconducting solenoids. Moreover, we are currently advancing this magnetic field source to its next iteration, which will operate in a persistent mode and incorporate a pioneering flux-pumping technique. Another departure from conventional traps involves the method of loading electrons where traditional techniques such as field-emission-points have been replaced by an approach harnessing the photoelectric effect to maximise deployability. Finally, we are pushing to the limit the detection system electronics by developing a broadband detection circuit with a simple resistor that enables the detection of single electrons as well as heavier particles, catering to a wide range of applications.

Speaker: Anna Migó

21 muCool: High brightness ultra-cold positive muon beam

The muCool project aims to develop an innovative device for generating low-energy, high-intensity, and high-quality muon beams for future high-precision experiments such as muon g-2 measurements, muonium spectroscopy, and muonium gravity studies. These experiments, involving muons and muonium atoms, hold significant potential for testing theoretical predictions of the Standard Model within a purely leptonic system.

The muCool device is designed to reduce the phase space of a standard positive muons beam by a factor of 10^10 with an efficiency of 10^-3 [1]. The muCool device is a cryogenic helium gas target with a complex electric field geometry inside the active volume, placed in a homogeneous magnetic field of 5T. Muons are transversely compressed by a combination of ExB drift and drift resulting from collisions with helium gas, as the collision frequency changes vertically due to the gas density gradient. Longitudinal compression is achieved through an electric potential minimum along the length of the muCool device. Combined transverse and longitudinal compression of the muon beam to sub-millimeter size and cooling to eV energies have been demonstrated recently [2]. To make the muCool device compatible with future muon experiments, the muon beam must be extracted from the target volume through an orifice. The extraction step poses a significant technical challenge in maintaining the helium gas density profile inside the muCool target while transitioning from a closed to open volume design. The upgraded design concept and simulation results for muon beam extraction will be presented.

[1] Belosevic, I., Antognini, A., Bao, Y. et al. "muCool: a next step towards efficient muon beam compression". Eur. Phys. J. C 79, 430 (2019). https://doi.org/10.1140/epjc/s10052-019-6932-z
[2] A. Antognini, N. J. Ayres, I. Belosevic et al. "Demonstration of Muon-Beam Transverse Phase-Space Compression". Phys. Rev. Lett. 125, 164802(2020). https://doi.org/10.1103/PhysRevLett.125.164802

Speaker: Joanna Peszka (ETH Zurich)

22 The NQCC’s Trapped Ion Team – technology development towards scalable quantum computing

The National Quantum Computing Centre’s Trapped Ion hardware team will host a variety of experimental architectures including different trap types, gate types, and atomic species. Initial internal work has been housing surface traps capable of high-fidelity, high-speed microwave gates in cryostats with a focus on modularity and autonomy for the laser and vacuum subsystems. These traps need to be loaded from ionising neutral atoms crossing the trapping volume. Laser ablation provides a thermally efficient method for neutral atom generation in cryogenics. But surface traps suffer from a weak trapping region, enabling the capture of only the slowest atoms in the ablation plume, which becomes an issue for plumes of high temperatures. The plume from various composition calcium targets is being characterised to determine the optimum conditions for efficient isotope generation. Compound targets were studied as isotopically-pure calcium is expensive and oxidises within an hour, which is not ideal for the repeated exposure involved in our system, which is optimised for rapid turn-around prototyping.

Speaker: Georgina Croft

23 Antihydrogen formation using a slow merge mixing scheme in ASACUSA’s Cusp trap

The ASACUSA collaboration at CERN plans to measure the ground-state hyperfine structure of a beam of antihydrogen to test CPT. To produce antihydrogen we slowly merged a positron and an antiproton plasma in a Penning-Malmberg trap with a cusped magnetic field. This ”smerge” method was pioneered by the ALPHA collaboration. We adjusted the rate at which the potential wells were merged from 0.1 s to 60 s finding that the slowest mixing produced the most antihydrogen. Interrupting mixing at different stages allowed the plasma space charge and radial extend to be determined as a function of time. White noise was used to heat the plasma and we studied the effect of positron temperature on antihydrogen formation.

Speaker: Marcus Bumbar (SMI)

ASACUSA_ECCTI.pdf

24 Phase noise in a 729 nm laser system

High-fidelity gates in trapped Calcium ions rely heavily on the stability of the main 729 nm qubit-manipulation laser, often achieved through locking it to a high-finesse cavity. The quality of the feedback loop governing this lock directly influences the noise of the laser that goes to the ions. This work focuses on presenting and characterizing the performance of a high-bandwidth triple-cascaded feedback loop, used for locking a 729 nm Ti:Sapphire laser to a high-finesse cavity. The phase noise of the system is quantified with in-loop and beat-note measurements. In addition, the different noise sources in the loop are examined and their influence discussed.

Speaker: Luka Milanovic

25 Microfabricated quantum processor unit with integrated optics

Trapped ions have shown great promise as a platform for quantum computing, with long coherence time, high fidelity quantum logic gates, and the successful implementation of quantum algorithms. However, to develop trapped-ion based quantum computers from laboratory setups to practical devices for solving real-world problems, the number of controllable qubits must be increased while improving error rates. One of the major challenges for scaling trapped-ion quantum computers is the need to switch from free space to integrated optics, to achieve lower drift and vibrations of light relative to the ion, and therefore more stable and scalable ion-addressing.

At Infineon and the University of Innsbruck, we are working on the integration of optical elements in surface ion traps, which are fabricated in industrial semiconductor facilities at Infineon. We use femtosecond-laser written waveguides to guide light in a glass-block that is manufactured on the chip's surface in wafer-level processes. The integrated waveguides eliminate vibrations between optics and the ion, and therefore reduce intensity fluctuations of the laser light at the position of the ion. Moreover, integrated waveguides can enable complex light routing to multiple trapping sites and make quantum information processors more robust and more scalable.

In this contribution, we present recent progress on fabrication of our iontrap.

Speaker: Jakob Wahl

26 Multiplexing of the Transport Through an X-Junction Ion Trap

When scaling up ion trap quantum processors the wiring of the large number of necessary control signals becomes a problem.
We present a concept for reducing the amount of control signals needed for the transport through the X-junction of a surface electrode ion trap. By using switching electronics, the signals are multiplexed and enable the control of multiple electrodes per incoming signal and therefore reducing the total amount. The key issues are finding the minimum number of signals that still allow the transport through the junction and the appropriate attribution of electrodes to the signals.

Speaker: Janina Bätge (Leibniz Universität Hannover)

27 Estimating the dynamical error map of single-qubit gates under non-Markovian phase noise

Quantum computers are inherently susceptible to the impact of noise. Precise characterization and effective noise mitigation techniques are imperative to progressively overcome the limitations posed by a noisy system such as enabling large-scale quantum computing. Motivated by this necessity, we introduce a newly developed microscopic model designed to provide a more compact parametrization of noisy single-qubit gates. Our analytic model is the first to go beyond the conventional practice of modelling depolarizing errors as the exclusive noise source, allowing us to predict the quantum processor’s performance even in regimes where the dynamics can be proven to be non-Markovian. This leads to an enhancement in describing the average channel infidelity with numerically exact evolution of noisy single-qubit gates by at least one order of magnitude, while the model's calculation requires solely the noise power spectral density as input.
To validate and compare the analytical model against experimental results, we apply quantum process tomography and randomized benchmarking techniques to a trapped-ion quantum information processor based on singly ionized Calcium-40. As expected, we find, that our model treating phase noise as the sole error source provides a close lower bound on the average gate infidelity obtained through randomized benchmark and quantum process tomography. Moreover, our model outperforms previous gate infidelity metrics based on filtered power spectral densities and serves as a promising extension to established quantum characterization, verification, and validation protocols. For example, it introduces a more efficient parametrization of gate sets characterized in gate set tomography, thereby significantly reducing the resource requirements associated with this demanding procedure.

Speaker: Alex Steiner (University Innsbruck)

28 Investigation of Plasmas in a Penning-Malmberg Trap for Gabor lens development

A Gabor lens, a type of plasma lens, utilizes the internal electric field of a trapped electron plasma to focus high energy positively charged particles, such as protons or ions [1]. This lens is formed within a non-neutral plasma confined by magnetic and electric fields in a Penning-Malmberg trap [2]. Compared to traditional magnetic lenses, Gabor lenses offer the potential for highly efficient and compact particle focusing. The focal length ($f$) of the Gabor lens depends on the strength of the radial field generated by the non-neutral plasma, which is determined by the plasma density ($n_e$), the kinetic energy of the positively charged particle ($U$), and the length of the plasma ($l$) via $\frac{1}{f}=\frac{e^2 n_e l}{4\epsilon_0 U}$ where $e$ is the magnitude of the electric charge of the electron, and $\epsilon_0$ is the permittivity of free space [3]. In this study, our aim is to attain a plasma density on the order of $10^{15}$ $m^{-3}$ to achieve a desired focal length of $1$ $m$ for the Gabor lens.

The practical implementation of an electron plasma faces challenges related to confinement, density, lifetime, and stability. We analyze these characteristics within our trapped electron plasma. Additionally, we present the results of applying a well-established manipulation technique—rotating electric fields—to control the plasma radius [4], aiming for longer plasma lifetimes and higher plasma densities. The attainment of prolonged plasma storage times and elevated plasma densities holds significant promise for advancing Gabor lens technology, crucial for a multitude of applications including particle accelerators and beam focusing systems.

[1] Gabor, D. (1947). A space-charge lens for the focusing of ion beams. Nature, 160(4055), 89-90.

[2] Fajans, J., & Surko, C. M. (2020). Plasma and trap-based techniques for science with antimatter. Physics of Plasmas, 27(3), 030601.

[3] Pozimski, J., & Aslaninejad, M. (2013). Gabor lenses for capture and energy selection of laser driven ion beams in cancer treatment. Laser and Particle Beams, 31(4), 723-733.

[4] Ahmadi, M., et al. (Alpha Collaboration). (2018). Enhanced control and reproducibility of non-neutral plasmas. Physical Review Letters, 120(2), 025001.

Speaker: Poram Ruksasakchai (Swansea University)

29 An end-cap Paul trap for precision spectroscopy

Trapped ions in radio-frequency Paul traps are one of the leading candidates for precision metrology at optical frequencies [1]. Ions can be confined and laser-cooled to their motional ground state [2], which minimizes the systematic shifts in the transition spectra. Current engineering challenges call for traps that improve the isolation of trapped ions from the environment and reach fractional uncertainties below 10−18 [3][4].
We present our design and indigenous fabrication of an end-cap Paul trap with reduced an-harmonicity in the trapping potential. With the help of COMSOL simulations, we have optimized the electrode dimensions while considering the achievable machining and alignment tolerances. We have developed a low-divergence oven to minimize the coating of the trap electrodes and successfully loaded a cloud of calcium ions into the trap [5]. I will present our trap characterization, custom imaging system, and preliminary results of our experiments with the ion trap.

Fluorescence of a single Calcium ion observed on EMCCD

Quantum jumps of a single Calcium ion

References
[1] Andrew D. Ludlow, Martin M. Boyd, Jun Ye, E. Peik, and P.O. Schmidt. Optical
atomic clocks. Reviews of Modern Physics, 87(2):637–701, June 2015.
[2] D. Leibfried, R. Blatt, C. Monroe, and D. Wineland. Quantum dynamics of single
trapped ions. Reviews of Modern Physics, 75(1):281–324, March 2003.
[3] Moustafa Abdel-Hafiz et al. Guidelines for developing optical clocks with 10−18
fractional frequency uncertainty. https://arxiv.org/abs/1906.11495.
[4] P. B. R. Nisbet-Jones, S. A. King, J. M. Jones, R. M. Godun, C. F. A. Baynham,
K. Bongs, M. Doleˇzal, P. Balling, and P. Gill. A single-ion trap with minimized
ion-environment interactions. Applied Physics B, 122(3):57, March 2016.
[5] Anand Prakash, Akhil Ayyadevara, E. Krishnakumar, and S. A. Rangwala. Low
divergence cold-wall oven for loading ion traps. Review of Scientific Instruments,
95(3):033202, March 2024

Speaker: Akhil Ayyadevara (Raman Research Institute)

30 Controlling the spontaneous emission of multiple trapped ions

We present a setup based on a phase spatial light modulator for manipulating the spatial characteristics of spontaneous emission of trapped ions. We delineate three specific applications where our setup demonstrates superior performance compared to current state-of-the-art solutions. Anticipated benefits include the potential to entangle more than two ions through a single photon detection event, the efficient channeling of all fluorescence photons emitted by an ion into an optical fiber, and the controlled modulation of visibility for distinguishable emitters. The setup controls the ions' emission in the far-field and can be adapted to most of the existing ion traps commonly used in quantum technology.

Speaker: Tommaso Faorlin (Universität Innsbruck)

31 Designing Robust RF Junctions for Register-Based Trapped-Ion Quantum Processors

Radiofrequency (RF) junctions enable two-dimensional structures within the QCCD architecture and are thus essential for scaling trapped-ion quantum processors. We discuss the design and optimization of RF junctions, highlighting implications for efficient through-junction ion transport. Further, we present an optimized RF junction in a surface-electrode trap and analyze its robustness concerning typical errors of the multilayer microfabrication process.

Speaker: Florian Ungerechts

32 Cavity assisted ion-photon entanglement

Trapped ions are one of the leading platforms for quantum networks. They benefit from long coherence times, high-fidelity state preparation, readout and gate operations. However, the number of ions that can be well-controlled in any individual trap is very limited. To circumvent this limitation ions can be distributed among many smaller traps that are connected via photonic links [1]. In this way, entanglement can be shared across traps facilitating the scaling of ion-based quantum computers to large numbers of qubits. To demonstrate efficient photonic links between ion traps, we couple single calcium-40 ions trapped in a linear Paul trap to an optical cavity formed by two macroscopic mirrors to generate photons. By driving two separate Raman transitions simultaneously the ion state can be entangled with the polarisation state of the photon [2]. By using a cavity to perform this ion-photon entanglement we aim to improve the rate of entanglement production. This ion-photon entanglement can then be employed to generate ion-ion entanglement across a quantum network.

[1] T. Ward and M. Keller, New J. Phys. 24 123028 (2022)
[2] A. Stute et al., Nature 485, 482 (2012)

Speaker: Ian Ford (University of Sussex)

33 Building a cryogenic quantum computing demonstrator based on trapped ions

Surface electrode ion traps are well suited for building a scalable quantum computer because ions trapped in a Paul trap can have long coherence times combined with high fidelities, and it is possible to move the qubits around in a 2-D surface. I will present our design for a cryogenic setup aimed at increasing the fidelity of state preparation and quantum gates. Our experiments allow us to use different ion traps featuring sections for loading and storing ions as well as junctions, interaction, and detection zones. We are building two setups, one based on 9Be+ logic ions together with 40Ca+ ions for sympathetic cooling and a second one based on 43Ca+ logic ions with 88Sr+ ions for sympathetic cooling. The experiment control system is based on the ARTIQ hardware/software stack. It controls the DC lines for the surface electrodes, RF electronics for the RF trap drive and also the AOMs, and microwave electronics which are used for driving single- and two-qubit gates via a microwave field.

Speaker: David Christoph Stuhrmann (Insitut für Quantenoptik, Leibniz Universität Hannover)

34 Imaging System Design for Trapped Ion Quantum Computing Demonstrators

Trapped ions are interesting in the field of quantum computing due to their exceptional qubit coherence times and high-fidelity gate operations. An imaging system is central to their functionality, as it plays a critical role in visualizing, understanding, and troubleshooting the workings of the ion trap. We design one such imaging system while keeping in mind the challenges that arise while tailoring it for cryogenic and vacuum-isolated trapping chips.

We focus on the evolution of our imaging system over different iterations of the experiment. This is done with the aim of highlighting the key challenges, possible solutions, and limitations that come with these assemblies. The design, in each case, is guided primarily by the desired values for resolving power and magnification. However, it is noted that there are new considerations that arise when practically working with the various optical elements and their physical limitations.

In summary, we shed light on the interplay between hardware components, theoretical principles, and experimental challenges. By discussing the current state-of-the-art and future prospects, this work aims to contribute to the continued advancement of imaging systems in quantum computing demonstrators.

Speaker: Radhika Goyal

35 Precision improvements for laser spectroscopy of anti-hydrogen in the ALPHA experiment

A high priority in the worldwide search for 'New Physics' involves testing violations of fundamental symmetries. In particular, one the largest remaining cosmological questions is why the observable universe is populated by only matter, rather than equal amounts of matter and antimatter. By comparing the results of precise laser spectroscopy of both matter and antimatter, CPT symmetry can be directly tested. Since the 1S-2S transition in hydrogen has been measured with unmatched precision [1], the ALPHA experiment has performed ultrahigh precision spectroscopy on the equivalent transition in antihydrogen [2]. By a combination of improvements in ion-trapping [3], laser cooling [4] and metrology instrumentation such as the use of a Caesium fountain clock, we aim to achieve the highest ever precision spectroscopy of the 1S-2S transition in antihydrogen. I will discuss the latest progress in the laser setup and the metrology techniques required to achieve such precision.

[1] C. G. Parthey et al. Improved Measurement of the Hydrogen 1S - 2S Transition Frequency. Phys. Rev. Lett. 107, 203001 (2011)

[2] M. Ahmadi et al. (ALPHA collaboration). Characterization of the 1S-2S Transition in Antihydrogen. Nature 557, 71-75 (2018).

[3] G. B. Andresen et al. (ALPHA collaboration). Trapped Antihydrogen. Nature 468, 673-676 (2010)

[4] C. J. Baker et al. (ALPHA collaboration). Laser cooling of antihydrogen atoms. Nature 592, 35-42 (2021).

Speaker: Virginia Rose Marshall (Aarhus University (DK))

36 Software Framework For Automated Calibration Of A Trapped-Ion Quantum Computer

Trapped ion quantum computers are transitioning from hands-on experiments to highavailability production systems. To achieve this, it is crucial to attain and maintain high operational fidelities of the quibt operations. Regular recalibration of system parameters is necessary due to the influence of fluctuating environmental factors. So far, this has been a labor-intensive and time-consuming task. In Mainz, we are developing a generalized software framework to automate these calibration tasks. Tight integration into the scheduler allows us to pause running measurements and recalibrate the system at any time. Detected system issues are resolved using backtracking methods. For the system currently in use, benchmarking demonstrated operational fidelities that match those achieved by trained personnel. Moreover, the calibration time was reduced from approximately one hour to eleven minutes. The implemented routines were confirmed to be robust against drifts surpassing typical daily fluctuations by an order of magnitude.

Speaker: Mr Andreas Conta (Universität Mainz)

37 High-Q room-temperature electron-ion Paul traps

While Paul traps are commonly used in ion trapping, electron trapping with Paul traps is a new line of advance, done only by few laboratories in the world [1–2]. It requires comparably high (GHz range) frequency, which creates a challenge for efficient power supply. Low input power, decreasing device heating, can be achieved by designing the trap as part of a resonator. We have developed a coaxial trap, designed for two signals at different frequencies to trap both electrons and ions. The high-frequency signal is delivered and amplified by a half-wave resonator. The trap is 3D-printed and shows a relatively good quality factor, more than 1 000.
Having a corresponding planar trap design, connected with resonating transmission lines, could improve optical access and make the trap possible to manufacture in standard CMOS methods [3] or direct laser inscription method on metal-plated glass substrate, developed by us [4]. We have filed a patent application for such trap design with a segmented ring electrode and resonating lines coupled with Marchand baluns. While there are still some challenges in having an efficient planar design, the development of both designs forwards using trapped electrons both in research and various quantum technological applications.

[1] Matthiesen, C.; Yu, Q.; Guo, J.; Alonso, A. M.; Häffner, H.: Trapping Electrons in a Room-Temperature Microwave Paul Trap, Physical Review X 11, 011019 (2021)
[2] Osada, A.; Tamiguchi, K.; Shigefuji, M.; Noguchi, A.: Feasibility study on ground-state cooling and single-phonon readout of trapped electrons using hybrid quantum systems, Physical Review Research 4, 033245 (2022)
[3] Kim, T. H.; Herskind, P. E.; Kim, T.; Kim, J.; Chuang, I. L.: Surface-electrode point Paul trap, Physical Review A 82, 043412 (2010)
[4] Antony, A.; Hejduk, M.; Hrbek, T.; Kúš, P., Bičišťová, R., Hauschwitz, P., Cvrček, L.: Laser-assisted two-step glass wafer metallization: An experimental procedure to improve compatibility between glass and metallic films, Applied Surface Science 627, 157276 (2023)

Speaker: Niklas Vilhelm Lausti (Charles University (Czech Republic))

38 Sub-Doppler cooling for ion-based qudits

An approach to overcome the obstacles of scalability of quantum computers is to use d-level (d>2) quantum systems, known as qudits which are inherently present in most quantum computing platforms. While qudits provide significant additional computational resources, the underlying theory on constructing qudit computational primitives and their experimental implementation remain widely unexplored. An essential first step for any computation requires sub-Doppler cooling of the qudits. Here, we design and simulate a cooling scheme for $^{176}$Lu$^+$ which forms a qutrit in its $^3D_1$ hyperfine levels.

Speaker: Katya Fouka (University of Amsterdam)

Tuesday 9 July

Antimatter

Convener: Joanna Peszka (ETH Zurich)

39 ALPHA-g data analysis: determining the gravitational acceleration of antihydrogen

The ALPHA-g experiment at CERN recently made the first direct observation of the effect of gravity on the motion of antimatter [1]. The result – that antihydrogen falls towards the Earth – is consistent with Einstein’s Weak Equivalence Principle.

In ALPHA-g, antihydrogen is produced by combining antiproton and positron plasmas, each confined in Penning-Malmberg traps. Antihydrogen is subsequently confined in an Ioffe-Pritchard magnetic trap with its axis aligned parallel to the Earth's gravitational field; an octupole provides radial confinement and two solenoids (one above and one below the trapping region), provide axial confinement. The gravitational potential adds to the magnetic potential; when the magnetic fields from the upper and lower solenoids are equal, the gravitational potential results in an up-down asymmetry in the total potential.

An imposed difference in magnetic field in the upper and lower solenoids, known as a bias, is delicately adjusted over a range of values. At each value of the magnetic bias, the magnetic fields of the solenoids are ramped down slowly compared to the antiatom motion, releasing the antihydrogen, and leading to annihilations on the walls of the apparatus which are detected by a position and time sensitive detector. If the imposed bias cancels the gravitational potential, antihydrogen escapes upwards or downwards with equal probability.

Determining the downward, $p_{\text{dn}}$, escape probability from observed annihilations is non-trivial because the efficiency with which antihydrogen annihilations are detected in the upper and lower regions may be different, some small fraction of antihydrogen escaping downwards may be detected in the upper region (and vice versa) and the precise number of trapped antihydrogen atoms is unknown. In addition, cosmic rays passing through the apparatus lead to a background annihilation rate which may also be up-down asymmetric.

A Bayesian method is employed to determine $p_{\text{dn}}$. The likelihood analysis assumes annihilations detected in the upper and lower regions are independently Poisson distributed, with Poisson mean expressed in terms of the relative detector efficiency, the efficiencies with which annihilations are detected in the incorrect region, the cosmic background annihilation rates, and $p_{\text{dn}}$. We solve for the posterior $p_{\text{dn}}$ using the Markov-Chain Monte-Carlo integration package, Stan [2].

Further, we determine the gravitational acceleration of antihydrogen and a statistical error by modifying the likelihood analysis described above to include results from simulations of the experimental procedure. In the modified analysis, $p_{\text{dn}}$ is replaced by the simulated probability of downward escape, which is a function of the antihydrogen gravitational acceleration.

Future increased precision measurements of antimatter gravity will involve transferring the trapped antiatoms to shallower confining potentials. Adiabatic cooling [3] during magnetic transfer will reduce antiatom loss and further increase sensitivity to gravity.

[1] Anderson, E.K., Baker, C.J., Bertsche, W. et al. Observation of the effect of gravity on the motion of antimatter. Nature 621, 716–722 (2023). https://doi.org/10.1038/s41586-023-06527-1
[2] Stan Development Team. 2023. Stan Modeling Language Users Guide and Reference Manual, 2.31. https://mc-stan.org
[3] D. Hodgkinson, On the Dynamics of Adiabatically Cooled Antihydrogen in an Octupole-Based Ioffe-Pritchard Magnetic Trap, Ph.D. thesis, The University of Manchester (2022).

Speaker: Danielle Louise Hodgkinson (University of California Berkeley (US))

Danielle_Hodgkinson_Presentation.pptx

40 Sympathetic cooling of a Be+ ion by a Coulomb crystal of Sr+ ions: a test bed for taming antimatter ions (GBAR)

The GBAR (Gravitational Behaviour of Antihydrogen at Rest) experiment at CERN, situated on the antiproton decelerator ring (AD), is aimed at investigating the free fall of antihydrogen atoms prepared at rest, as suggested by J. Walz and Th. Hänsch [1]. This experiment employs two trapped ions: one is a Be+ ion cooled via laser, while the other, an Hbar+ ion, undergoes cooling through interactions with the Be+ ion (sympathetic cooling).

We are developing a test-bed experiment designed to explore sympathetic cooling of a light ion using a cloud of laser-cooled heavy ions, mimicking the conditions anticipated in the GBAR project [2]. The experimental setup involves the pairing of 88Sr+ (laser-cooled ion) and 9Be+ (sympathetically-cooled ion). The choice of these ions offers two advantages: the ability to optically address the 9Be+ ion for thermometry measurements and their mass ratio (88/9 ≈ 9.8) closely resembling that in the GBAR project (9/1).

Preliminary experimental results [3] demonstrate sympathetic cooling of 9Be+ ions by laser-cooled 88Sr+ ions, forming a Coulomb crystal. Detection of sympathetically cooled ions relies on analyzing Coulomb crystal images, revealing dark areas where non-laser-cooled Be+ ions reside. Molecular dynamics simulations showed strong spatial segregation for both species, due to their high mass ratios [4].

However, the initial experiment did not include laser addressing of the 9Be+ ions for measuring cooling dynamics and control over the initial energy of Be+ ions. The next stage of the project therefore involves adding the 313nm laser for addressing Be+ ions and utilizing a 2-zone trap to control the initial energy of a single Be+ ion. This will enable us to measure for the first time the capture dynamics of a light ion by a Coulomb crystal and to follow its cooling over several decades (typically from 10000K to mK). We will compare these measurements with numerical simulations [4].

Initially, only Sr+ ions were employed to validate trapping and cooling conditions, characterize photon collection optics, and test ion transport protocols between trapping zones. A method utilizing Doppler recooling was developed to characterize the initial energy of Sr+ ions upon arrival in the target trap. Subsequently, using the Be+ ion cooling laser at 313 nm, it will be possible to cool a single Be+ ion and transport it with controlled kinetic energy to the second trapping zone, already loaded with a Sr+ Coulomb crystal. The kinetic energy loss of the Be+ ion is quantified by measuring laser-induced fluorescence rate at resonance, which produces no laser cooling or heating. Thermalization of the light ion via coulomb interactions will then be studied for different heavy-ion crystal temperatures, shapes and ion numbers.

REFERENCES
[1] J. Walz and T. Hänsch, General Relativity and Granvitation, (2004) 561
[2] P. Perez and Y. Sacquin, Classical and Quantum Gravity, 29 (2012)
[3] A. Douillet et al., 1st North American Conference on Trapped Ions (NACTI 2017) Boulder, USA, 2017
[4] N. Sillitoe et al., JPS Conf. Proc. 18, 011014 (2017)

Speaker: Derwell Drapier

Présentation ECCTI Derwell.pdf

41 Studies of highly charged ions formed using antiprotons at AEgIS

Antimatter Experiment: gravity, Interferometry, Spectroscopy (AE$\bar{\hbox{g}}$IS) achieves pulsed production of antihydrogen using a charge-exchange reaction between antiproton and Rydberg positronium (an electron and a positron in a bound state). The AE$\bar{\hbox{g}}$IS experiment is used to probe antimatter bound systems for measurements of gravitational free fall and precision studies of positronium. More recently a new program has been started which focuses on the controlled formation and studies of antiprotonic atoms - a bound state consisting of antiproton in an orbit around a matter nucleus.

Ongoing developments strive to achieve controlled formation of antiprotonic atoms by co-trapping anions with cold antiprotons. Then one laser would neutralize the ions and subsequently another laser would excite the formed neutral atom to a Rydberg state for a charge-exchange reaction with the antiprotons.

The controlled formation of antiprotonic atoms within the trap allows a detailed spectroscopic study of antiprotonic bound states in a trap.
In the case that an antiprotonic atom is formed, the antiproton would cascade down the electronic energy levels causing emission of Auger electrons and x-rays until the antiproton is close enough to annihilate on the nucleons, resulting in highly charged nuclear fragments. Capturing highly charged positive ions would be of further interest for nuclear structure studies.

A new procedure for proof-of-principle measurement was developed. Low pressure nitrogen gas was introduced into the AE$\bar{\hbox{g}}$IS apparatus. Antiprotons were then trapped inside the apparatus and a nested trap was formed to capture positive ions. Subsequently, the antiprotons were released, and the nested trap was reshaped for time-of-flight (TOF) measurement. Then, the ions in the nested trap were released, and TOF spectra were captured using an MCP. To analyze the TOF spectra, we compared them with simulations. This work has shown that it is possible to trap ions formed by the antiproton interaction with a gas and use the AE$\bar{\hbox{g}}$IS apparatus as a TOF spectrometer capable of giving insights into mass to charge ratios of the ions.

Speaker: Mr Valts Krumins (University of Latvia (LV))

ECCTI2024_Valts.pdf

ECCTI2024_Valts.pptx

42 Towards a 10-fold improved measurement of the antiproton magnetic moment

The standard model of particle physics provides one of the currently best descriptions of nature but fails to account for the asymmetry between matter and antimatter that is observed on cosmological scales. One way to investigate this problem is the test of CPT-Invariance by comparisons between fundamental proton and antiproton properties. [1]

The BASE collaboration is specialized in the use of advanced Penning trap setups as well as cryogenic superconducting detection systems with single particle resolution to perform high precision measurements on protons and antiprotons. Past measurements include the comparison of antiproton and proton charge-to-mass ratio with a fractional precision of 16 parts per trillion (ppt) [2] and the antiproton g-factor with a fractional precision of 1.5 parts per billion (ppb) [3]. This 3000-fold improvement of the g-factor precision helps to constrain possible CPT-odd interactions and sets limits on possible exotic particle interactions [4]. BASE is dedicated to further improving the precision of these measurements by continuously refining its Penning trap setup and is aiming to increase the g-factor precision to the 100 ppt level.

This contribution will give an overview of the BASE antiproton experiment located at CERN and aims to explain the unique challenge that sub-ppb precision g-factor measurements in accelerator halls pose. Focus is put on the understanding, characterization and if possible, the suppression of systematic corrections due to imperfections in the magnetic and electric fields.

[1] Hori, Masaki, and J. Walz, Progress in Particle and Nuclear Physics 72 (2013)
[2] M. J. Borchert et al., Nature 601, 35 (2022)
[3] C. Smorra et al., Nature 550, 371 (2017)
[4] Smorra, C., Stadnik, Y.V., Blessing, P.E. et al., Nature 575, 310 (2019).

Speaker: Bela Peter Arndt (Max Planck Society (DE) / GSI Helmholtzzentrum für Schwerionenforschung GmbH)

ECCTI_bela_p_arndt.pdf

ECCTI_bela_p_arndt.pdf

ECCTI_bela_p_arndt.pptx

Coffee break

eccti_coffeebreaks.pdf

eccti_coffeebreaks.pptx

Quantum Technologies

Convener: Marion Mallweger

43 Towards Sideband Cooling and Thermometry on an X-Junction Surface Trap with Integrated Current Carrying Wires

Trapped ions have proved to be a promising way of realising a large-scale quantum computer. They allow for simple reproducibility and modular architectures which is crucial for a scalable, universal quantum computer. Our blueprint for a trapped-ion based quantum computer outlines operating with global microwave (MW) fields to dress the ground-state hyperfine manifold of 171Yb+ ions [1].

Borrowing knowledge from the semiconductor industry, we have produced microfabricated ion traps with embedded current-carrying wires (CCWs) which provide a controllable, high magnetic field gradient [2]. By applying a stable, fast switching current source to these wires, we measure an accurate local magnetic gradient using Ytterbium 171 and demonstrate the current working operation of this chip. The local magnetic gradient is important to provide regions of the chip where entanglement is performed, and regions where qubits can be held in a memory zone, which do not utilise magnetic gradients.

Static magnetic gradients coupled with global microwave fields enable high spin-motion coupling parameters. This allows spin-motion coupling which allows more accurate energy measurements to be performed on the motional sidebands and track the heating rate of the ion which is very important for measurements of gate infidelities and characterizing transport and reconfiguration protocols. With this scheme, we are then able to perform sideband cooling to the motional ground state, which is required for certain gate schemes, and to perform diabatic transport.

[1] B. Lekitsch, S. Weidt, A. G. Fowler, K. Mølmer, S. J. Devitt, C. Wunderlich, and W. K.Hensinger, “Blueprint for a microwave trapped ion quantum computer”, Science Advances 3 (2017).
[2] M.S.Brown et. Al. Fabrication of surface ion traps with integrated current carrying wires enabling high magnetic field gradients (2022) Quantum Sci. Technol. 7 034003

Speaker: Sahra Ahmed Kulmiya

Towards Sideband Cooling and Thermometry on an X-Junction.pdf

Towards Sideband Cooling and Thermometry on an X-Junction.pptx

44 Test and characterization of multi layer ion traps on fused silica

Quantum computing has emerged as a promising frontier with the potential to revolutionize computation by effectively tackling classically intractable problems. Among the various platforms for realizing a universal quantum computer, trapped ions have demonstrated their capabilities, allowing for quantum gate operations on quantum bits (qubits) by manipulating single or multiple ions. This approach offers notable advantages such as low error rates and long storage times [1]. However, the pursuit of a universal quantum computer inherently demands the scaling up of qubit numbers, which presents a significant engineering challenge. One such challenge is the construction of ion traps capable of storing many ions while keeping the qubit-to-qubit connectivity sufficiently high.
To tackle this scalability problem, our primary focus is on an industrially microfabricated surface ion trap designed to accommodate larger numbers of ions arranged in a two-dimensional grid [2]. Furthermore, we have developed an electrical wafer test as an example of how increasingly complex ion traps can be tested before their integration into a setup.
We use a surface ion trap with the capacity to confine 18 ions within two adjacent 1D crystals. The trap comprises three aluminum layers separated by silicon oxide, constructed on a fused silica substrate manufactured at the industrial fabrication site of Infineon Villach. Additionally, the ion trap incorporates an integrated resistance-based temperature sensor with sensitivity of 2.5 Ohm/K @ 10K to monitor the ion trap during operation. Furthermore, a comprehensive room temperature electrical wafer test concept comprising 540 measurements per chip was developed. This verifies the functionality of the trap before insertion in the setup. Heating rates below 10ph/s at an axial frequency of 1.2MHz on different trapping sites were measured to benchmark the trap in a cryogenic environment. The presentation will cover the trap concept, the electrical wafer test procedure, the characterization of the temperature sensor, and the results achieved with the ion trap in a cryogenic setup.

[1] C. Bruzewicz, Trapped-ion quantum computing: Progress and challenges, arXiv:1904.04178
[2] P. Holz, Two-dimensional linear trap array for quantum information processing, arXiv:2003.08085

Speaker: Matthias Dietl

Dietl__presentation.pptx

45 Industrially fabricated ion trap chips for radial coupling experiments

We present and discuss industrially fabricated ion trap chips [1, 2] on the dielectric substrates Fused Silica and Sapphire.

Surface ion trap chips offer a promising platform for the scaling of ion trap quantum computers. We investigate shuttling in the radial direction as element of a scalable architecture [1]. For this, we present chips that are designed to trap ions in two-well potentials in the large separation and in the radial coupling regimes. The chips presented are capable of trapping ions or ion chains in separate rf potential wells. The design parameters of a surface ion trap in the radial coupling regime with fixed ion height and ion-ion distance are investigated. Based on this, we present improved trap designs. We discuss the simulation, design and fabrication challenges involved in creating such chips. The traps are or will be fabricated on single- and multi-layer stacks. The fabrication on multi-layer stacks enables a more complex electrode geometry and therefore more complex scalable ion trap layouts.

The ion traps are fabricated on the dielectric substrates Fused Silica and Sapphire, which are ultra-wide-bandgap materials and therefore promise excellent resilience against UV light and low rf losses. The status of industrial microfabrication on these materials is discussed, with a focus on the challenges of fabrication on different substrate materials and the fabrication of multi-layer stacks.

[1] Ph. Holz, S. Auchter et al., Adv. Quantum Technol. 3, 2000031 (2020)
[2] S. Auchter, C. Axline et al., Quantum Sci. Technol. 7, 035015 (2022)

Speaker: Michael Pfeifer (University of Innsbruck, Infineon Technologies Austria AG)

Talk_Pfeifer_final.pdf

Talk_Pfeifer_final.pptx

46 Novel ion trap with fibre cavity integration

The ion trap serves as a quantum platform with the potential to facilitate the realization of a scalable, fault-tolerant quantum computer, coupled with a straightforward photonic interface for connection to the so-called quantum network. In this system, multiple ions can be trapped within a single trap and individually controlled via laser manipulation. However, practical implementation faces several challenges, including low photon collection efficiency. Addressing this issue, integrating an optical cavity and establishing strong coupling with the ions in the trap emerges as a potent solution[1], aligning with our ultimate objective.

In this study, we have designed a prototype of a monolithic trap, characterized as a linear Paul trap. Notably, the trap can be monolithically fabricated, with the blades supplying distinct electric signals being insulated from one another through a trench structure.

The first trap has been fabricated using the selective laser etching method (SLE). Subsequently, we successfully endeavoured to trap both individual ions and ion chains within the trap and are currently engaged in the process of acquiring ion spectroscopy data.

However, during the implementation, several potential improvements are spotted, thus, the second generation has started to be designed.

In the second-generation trap, a significant modification involves the central section, where the endcap transitions into a spherical shape to enhance DC trapping efficiency. Additionally, four DC compensation blades have been incorporated to counterbalance the effects stemming from the cavity substrate. Comsol simulations on the trapping potential have been conducted to determine optimal compensation voltage and the distance between the blade and ion axis.

Furthermore, due to the reduction in the number of cavity modes resulting from the decreased mode volume, the size of the trap has been scaled down to approximately 1cm x 1cm, allowing for closer placement of the cavity mirrors. Another benefit of this reduction in size is the ability to shrink the cavity substrate accordingly, thereby enhancing the mechanical stability of the cavity system.

Moreover, the intricate wiring required to transmit electric signals via the feedthrough from outside of the chamber will be replaced by a neat printed circuit board (PCB) positioned beneath the trap itself. This PCB comprises two copper layers insulated by a dielectric layer, and the trap will be wirebonded to the PCB using gold wires. To create additional space for optical access, we intend to implement a type of PCB known as a rigid-flex PCB. In this configuration, the rigid part mirrors a standard PCB, while the flexible part, composed of polyimide, is foldable.[2] Leveraging this foldable feature, multiple dimensions within the chamber can be utilized to construct the most suitable configuration for laser beam alignment.

As of the conference date, the fabrication of the prototype for the second-generation trap is anticipated to be completed, as well as the final assembly with the new PCB.

[1]Takahashi, Hiroki, et al. "Strong coupling of a single ion to an optical cavity." Physical review letters 124.1 (2020): 013602.
[2]Sterman, Yoav. PCB Origami: Folding circuit boards into electronic products. Diss. Massachusetts Institute of Technology, 2013.

Speaker: Zhenghan Yuan

ECCTI Zhenghan Yuan.pdf

ECCTI Zhenghan Yuan.pptx

47 Monolithic Segmented 3D Ion Trap

We demonstrate the fabrication and operation of a linear Paul trap made from a single piece of fused silica. The glass is machined using a femtosecond laser assisted etching technique and subsequently coated with a conductive layer of gold. T-shaped trenches along the surface of the glass ensure insulation between neighbouring electrodes, without the use of shadow masks during the coating procedure. The monolithic design does not require alignment of individual components, reducing potential geometric imperfections and resulting anharmonicities.
The trap is designed to contain up to 50 ions for quantum computing and simulation experiments. The width of the electrode segments is optimised to facilitate strings of equidistant ions, which we demonstrate by confining strings of calcium ions. The trap geometry is versatile and designed to be suitable for other applications. Notably, the highly symmetric structure and axial access enables trapping of externally generated ions for spectroscopic experiments.

Speaker: Edgar Brucke (ETH Zurich)

2024_ECCTI_monolithic_trap_talk.pptx

Lunch break

Lab tours

Skill session: Structuring your research paper by Jean-luc Doumont

Coffee break: Conference Photo

eccti_coffeebreaks.pdf

eccti_coffeebreaks.pptx

Poster session

48 D-5/2 to P-3/2 spectroscopy on a single trapped Ba-138 ion

Performing quantum spectroscopy on a single trapped $^{138}\mathrm{Ba}^{+}$ ion to determine D$_{5/2} - $P$_{3/2}$ transition frequency. A single isotope selected ions was loaded into a cryogenically cooled linear Paul trap which is subjected to a stable magnetic field. With an ion in the ground state, a narrow 1762 nm fiber laser was employed to address the quadrupole S$_{1/2} - $D$_{5/2}$ transition, preparing the ion in either the $m_j = -5/2$ or the $m_j = 5/2$ 'shelved' substate. The D$_{5/2} - $P$_{3/2}$ probe pulse was supplied by a 635 nm commercial diode laser cryogenically cooled to produce 614 nm light. Its optical frequency was stabilised by a wavemeter which in turn was calibrated against 633 nm, 650 nm, and 729 nm light sources simultaneously referenced to a frequency comb. Completed deshelving transitions were detected by observing 494 nm fluorescence induced by a Doppler cooling beam addressing the S$_{1/2} - $P$_{1/2}$ transition assisted by 650 nm repumper light addressing the D$_{3/2} - $P$_{1/2}$ transition. The D$_{5/2} - $P$_{3/2}$ resonance frequency was determined as the average of the substate transitions to 487.990 056(2) THz.

Speaker: René Munk Thalund (Ion Trap Group, Department of Physics and Astronomy, Aarhus University)

49 Microfabrication of surface ion traps for operation with Strontium Rydberg ions

Recently, using Rydberg-states for gate operation in trapped ions has been shown to greatly reduce two qubit gate times down to 700ns [1]. Those experiments were performed in a macroscopic Paul trap at room temperature. We propose to perform similar experiments but in a cryogenic environment as well as on a of surface ion trap chip that is industrially microfabricated at Infineon Technologies [2,3]. This will prove further scalability of this gate scheme. We will give details of the planned experimental setup and show its current status.

As UV-Lasers are needed for the Rydberg gate operation, we discuss material and design choices for making our ion trap resilient against radiation down to a wavelength of around 240nm and show successful microfabrication of an ion trap on a sapphire substrate. We show first results from surface characterization methods like the measurement of photocurrent when illuminating trap surfaces with UV-light. This will be used to further improve the quality of our trap metallization.

[1] Chi Zhang et al., Nature 580, 345-349 (2020)

[2] Ph. Holz et al., Adv. Quantum Technol. 3, 2000031 (2020)

[3] S. Auchter et al., Quantum Sci. Technol. 7, 035015 (2022)

Speaker: Simon Schey (Stockholm University and Infineon Technologies Austria AG)

50 Deployable ion trap quantum network node

Trapped ions provide a promising platform for building a Europe-wide quantum internet where quantum network nodes are separated by several hundreds of kilometres. Coherent ion-photon interfaces, consisting of a linear Paul trap with an integrated cavity, exist for more than a decade [1], and are capable to act as a quantum processor, telecom-wavelength quantum repeater [2] and quantum memory [3]. To pave the way towards a quantum network based on trapped ions, we develop and construct, for the first time, a fully integrated rack-mounted ion-photon interface that we call the “deployable node” which means that the node can in principle be transported to and operated at a remote location, without requiring laboratory conditions, e.g. a data centre. The node will be capable to provide laboratory conditions on its own and can be connected to other nodes via telecom-wavelength fibre. The ion-photon interface is given by a near-concentric 20mm long optical cavity and based on the proven design of Ref. [4]. Here, I present the design and the first results of the characterisation of the new setup.

[1] Stute, A., et al. "Tunable ion–photon entanglement in an optical cavity." Nature 485.7399 (2012): 482-485.
[2] Krutyanskiy, Victor, et al. "Telecom-wavelength quantum repeater node based on a trapped-ion processor." Physical Review Letters 130.21 (2023): 213601.
[3] Drmota, Peter, et al. "Robust quantum memory in a trapped-ion quantum network node." Physical Review Letters 130.9 (2023): 090803.
[4] Schupp, J., et al. "Interface between trapped-ion qubits and traveling photons with close-to-optimal efficiency." PRX quantum 2.2 (2021): 020331.

(For this project, we collaborate with the local company Alpine Quantum Technologies (AQT) with expertise in rack-mounted ion trap systems.)

Speaker: Pascal Wintermeyer (University of Innsbruck - Faculty of Experimental Physics)

51 Advancements in the cryogenic apparatus design for trapped ion quantum computing within the ATIQ project

Trapped-ion quantum systems are promising candidates for future quantum computing applications. Further advancements in scalability, reliability, and improved gate fidelity are of utmost importance. In the ATIQ consortium, we enhance our cryogenic apparatus design by transitioning to 43Ca+ as our logical qubit ion. This shift will pave the way for integrating waveguides into our existing trap architecture. Since the alignment of laser beams and the quantization axis defined by the magnetic bias field are paramount, a new tiltable magnetic field array was designed to ensure optimal alignment.
Additional advancements include a novel integration of the trap chip via a socket. By circumventing the limitations imposed by traditional gold wire bonds, we open up new possibilities. Specifically, this approach enables higher-density direct current (DC) connections and facilitates more sophisticated chip layouts.
Within the consortium, the new compiler will be incorporated, bridging the gap between higher-level algorithm languages (such as Qiskit) and the common ARTIQ experiment control code, thereby enabling broader access to quantum computing demonstrators.

Speaker: Tobias Pootz

52 Industrially microfabricated 3D ion traps for quantum information processing and metrology

Building a useful fault tolerant quantum computer requires precise and coherent control over several thousands of qubits. While the trapped ion platform has demonstrated such control over a limited number of ions, scaling to larger qubit numbers requires microfabricated trap chips characterized by a high degree of integration and process stability which can usually only be achieved within industrial facilities. This includes overcoming challenges regarding multi-metal layer stacks for complex electrode designs and incorporating photonic layers for ion addressing. Also, ion traps for quantum metrology applications such as chip-scale optical atomic clocks will benefit from precise and controlled fabrication processes.

In the BMBF project “ATIQ”, we are developing ion traps with integrated waveguides based on patterned dielectric thin films. Fabrication of the photonic layer and electrode metallization will be done by “Black Semiconductor” and Infineon Technologies, respectively. Testing of the trap chip will be carried out at PTB. We are also working towards 3D trap architectures based on dielectric substrates for compact and reliable ion clocks. To fabricate these 3D traps, we use state-of-the-art MEMS wafer bonding technology while also investigating new processes for microstructuring Through-Glass-Vias (TGVs) together with our project partner “LPKF Laser & Electronics”.

Speaker: Max Glantschnig (Infineon Technologies Austria AG)

53 State-preparation and quantum control of polyatomic molecular ions

Trapped molecular systems are excellent tools for precise quantum control, offering a wide range of applications in quantum computing, precision spectroscopy, tests of fundamental physics and state-to-state chemistry [1,2]. However, these systems have complex internal energy-level structures and in addition, they lack readily accessible closed cycling transitions which makes their state preparation, laser cooling, quantum control and coherent manipulation difficult.
Currently, in our lab, we utilize quantum logic spectroscopy to co-trap molecular ions such as $\text{N}_2^+$ with atomic ions such as $\text{Ca}^+$ ions in an RF ion trap [1,2]. $\text{N}_2^+$ is prepared in its ground rovibrational state, sympathetically cooled using Doppler cooled $\text{Ca}^+$ atomic ions and non-destructively state detected using quantum logic spectroscopy [3].
Quantum-logic schemes have proved to be useful for the cooling, for the non-destructive detection of the quantum states and for the coherent manipulation of diatomic molecular ions which was otherwise challenging [1,4,5]. Our goal is to work towards the quantum control of complex polyatomic molecular systems and further understand their chemistry, spectroscopy and collision dynamics.

References:
[1] M. Sinhal et al. Science 367.6483 (2020)
[2] M. Sinhal et al. p. 305 ff. in "Photonic Quantum Technologies: Science and Applications", ed. M. Benyoucef, Wiley-VCH 2023
[3] A. Shlykov et al. Adv. Quantum Technol. 2300268 (2023)
[4] C.W. Chou et al. Nature 545.7653 (2017)
[5] F. Wolf et al. Nature 530.7591 (2015)

Speaker: Nanditha Sunil Kumar (Universität Basel, Switzerland)

54 Twenty-zone surface ion trap with fully integrated photonics

One of the obstacles in scaling up trapped ion quantum computing is the increasing number of free-space lasers with increasing numbers of ions. These lasers are necessary for cooling the ions as well as performing quantum state manipulation and readout. In QCCD architectures, where ions are moved in two-dimensional trap arrays, individual addressing by free-space lasers further increases the system complexity. A promising avenue to address this challenge is the delivery of light through on-chip integrated waveguides, as previously demonstrated in the Home group at ETH Zurich [Mehta, 2019] for infrared light. Jointly with the ETH team, our group at PSI, is exploring this approach now in a 2D array that incorporates both UV and infrared light delivery through integrated photonics, combining Si3N4 and Al2O3 for the first time in an ion trap.

Speaker: Tereza Viskova

55 Towards a two-dimensional ion crystal immersed in an ultracold atomic cloud

In experiments with trapped ions, individual particles are separated due to the Coulomb force. This feature makes the system especially suitable for studying few-body systems. In contrast, a large number of neutral atoms can reach quantum degeneracy. In our laboratory, we are developing a hybrid system of trapped Barium ions and neutral Lithium atoms. In our previous work, we have investigated a rotational melting of a two-dimensional Coulomb crystals in a Paul trap [1]. Recently, we have developed a system which the rotational speed of a two-dimensional ion crystal can be controlled. What is more, by tuning the trap frequency ratio in the 2D trapping plane, we have experimentally observed that a two-dimensional ion crystal consisting of a specific number of particles have multiple stable configurations which enables us to create a bistable coulomb crystal [2]. In case of an ion crystal consisting of 6 ions, the two configurations can be expressed as a pentagon shape with one ion at the center and a hexagon shape with no ion at the center of the crystal. Eventually, we aim at placing a two-dimensional crystal of ions inside an ultracold background gas of neutral Lithium to observe these phenomena in the quantum regime. Our plan is to transfer ions from a Paul trap to an electro-optical trap [3] before mixing ions with neutral atoms to avoid any heating from micromotion, leading to an efficient sympathetic cooling of the ions by the atoms. At the conference, latest results of our research will be presented.
[1] L. Duca, N. Mizukami, E. Perego, M. Inguscio and C. Sias, Phys. Rev. Lett. 131, 083602 (2023).
[2] G. Pupillo et al., arXiv:0904.2735v1 (2009).
[3] E. Perego et al., Appl. Sci. 2020, 10(7), 2222 (2020).

Speaker: Naoto Mizukami (INRiM, LENS and Politecnico di Torino)

56 Enhancing Robustness in Ion Trap Quantum Logic through Optimal Control of Two-Qubit Operations

In quantum information processing, the controlled and isolated environment provided by cold trapped ions is pivotal for extending coherence times and reducing error rates, thus advancing the capabilities of quantum computing. We use two calcium ions in a string confined in a radio-frequency trap and prepared in their ground state of motion (with motional quantum number close to zero) using the sideband cooling technique. In order to showcase high-fidelity quantum logic gates employing two trapped ions, our qubit configuration utilizes the quadrupole electron transition at 729 nm or the Raman transition between the Zeeman sublevels of the ground state S1/2 to probe the Zeeman qubit. In attempts to improve the fidelity of the quantum logic gate, we implement optical filtering of unwanted frequency components in the laser driving the Raman interaction, thus enhancing coherence times by reducing scattering effects. Additionally, efforts are directed towards compensating for magnetic field fluctuations, primarily induced by the mains supply at 50 Hz, aiming to further extend coherence times and enable experiments without the necessity of line triggering. We aim to improve the fidelity of a standard Mølmer-Sørensen gate and subsequently demonstrate the resilience of strongly-coupled polychromatic gate beyond the Lamb-Dicke regime.
These developments represent significant strides towards more robust and reliable two-qubit quantum gate operations. The combination of improved laser spectral purity, long coherence times, better magnetic field compensation, and advanced gate designs paves the way for higher fidelity quantum computations.

Speaker: Kanika Kanika

57 Towards large scale quantum computing – a many qubit ion trap at room temperature

Extensive research is dedicated to large-scale quantum computing, still which one optimal platform is superior for general-purpose quantum computers is not yet clear. Trapped ions, serving as qubits, demonstrate superior gate fidelity and coherence times. However, current systems predominantly operate with a limited number of qubits. We are working to construct a new design that supports a linear chain comprising up to 50 ions, each individually addressable, thus offering a flexible platform with numerous qubits and precise control. The core of our system is a three-dimensional ion trap constructed from gold-coated laser-machined glass, operating in ultra-high vacuum conditions at room temperature. Individual addressing is facilitated through a waveguide array. Among its applications, our system contributes to research on large distance error correction, paving the way for fault-tolerant quantum computation. Its precise control proves advantageous for simulating complex Hamiltonians, enabling large-scale quantum simulations. Additionally, the trap's segmented electrodes permit the division of the ion chain into multiple segments, facilitating parallel quantum processing.

Speaker: Paul Venetz

58 Towards state preparation, readout, and control of polyatomic molecular ions using quantum logic spectroscopy

Molecular ions offer more degrees of freedom than atomic ions. These larger Hilbert spaces are rich and interesting landscapes to explore, possibly enabling quantum information applications such as quantum error correcting (QEC) schemes not available in atomic ions. This requires efficient and precise control of the molecular ion states. Co-trapping a molecular ion with an atomic ion facilitates state preparation and readout via quantum logic spectroscopy. Our group aims to use calcium-based molecules, e.g., CaH+ or CaOH+, co-trapped with a 40Ca+ ion for exploring these applications in QEC and precision spectroscopy. Coherent control within a rotational manifold of a molecular ion can be achieved by driving two-beam Raman transitions, as direct transitions between the sublevels in the same manifold are forbidden by selection rules

Speaker: Mariano Isaza Monsalve (University of Innsbrcuk)

59 Demonstration of 2D connectivity for a two-dimensional ion trap architecture

We investigate scalable ion trap architectures for quantum computing and simulation, where independent ion strings are located in distinct lattice sites (or potential wells) in a 2D array of RF traps. Distinct ion strings are coupled via their dipole-dipole interaction. Full 2D connectivity is achieved tuning the distance between adjacent potential wells along two orthogonal directions: One direction (axial) is achieved controlling DC voltages, and the other (radial) controlling RF fields. In this work we demonstrate the building blocks of such an architecture using two surface ion traps. With the first, we demonstrate DC shuttling-based well-to-well coupling rates up to 40 kHz between ion-registers of up to 6 ions each, and phonon exchange between ion strings at the quantum level. With the second, we characterize RF transport of ions along the radial direction, and measure well-to-well coupling rates up to 15 kHz. These results provide an important insight into the implementation of fully controllable 2D ion trap lattices, and pave the way to the realization of 2D logical encoding of qubits.

Speaker: Marco Valentini (Universität Innsbruck)

60 Floquet-Gibbs states in laser-driven atomic systems

Periodically driven quantum systems in a thermal environment generically settle to a Floquet-Gibbs state in a rotating frame, which is stable on long-time scales, provided that the driving frequency is high enough. However, in laser-driven atomic systems, which is a versatile platform for quantum technologies, the situation is typically more complicated, since the corresponding Hamiltonian is time-independent only in the rotating frame of the laser. If such systems are exposed to periodic variations of external parameters, their actual Hamiltonian usually becomes a quasi-periodic function of time. It is then no longer clear whether a generic stationary state exists and how it can be described, even in the high-frequency limit. We argue that systems of this type approach a stable Floquet-Gibbs state in an interaction picture that is connected to the Schrödinger picture by a quasi-periodic unitary transformation, provided that the laser frequency and the additional driving frequency are well separated and large compared to both the typical Bohr frequencies of the bare system in the rotating frame, and the typical energy exchanged in single-photon system-bath interactions. The Floquet-Gibbs state is determined by the temperature of the reservoir and an effective Hamiltonian that can be obtained from a Floquet-Magnus expansion. To demonstrate the validity of our arguments, we compare the exact solution of the time-dependent Redfield equation for a generic many-body system composed of Rydberg atoms or ions with the corresponding Floquet-Gibbs state.

Speaker: Wilson Santana Martins (Universität Tübingen)

61 Design and Implementation of a Microwave-Based Rubidium Atomic Clock System

At the forefront of precise time measurement, atomic clocks stand as essential tools, offering unparalleled accuracy crucial for a multitude of applications in radio astronomy, navigation systems, telecommunications and scientific research. The aim of this project is to develop a laboratory-scale atomic clock based on a Rubidium gas cell, which is exposed to microwave radiation and illuminated by a laser source. The purpose of undertaking this research is to develop expertise in atomic time keeping techniques.

The research will commence with an in-depth exploration of atomic physics principles fundamental to atomic clock development, alongside investigations into atomic interactions with electromagnetic radiation. Subsequently, spectroscopic experiments will be conducted to precisely determine the transition frequency between the hyperfine ground states in rubidium atoms. Investigations in microwave cavity design and geometries will also be conducted. Thereafter, simulation software will
be used to realize the design of a microwave cavity with a geometry optimized for maximum interaction with the Rubidium atoms, to achieve high sensitivity and accuracy in the atomic clock.

Stable microwave signals will be generated to drive the atomic transitions. A local oscillator will provide a stable reference signal for phase-sensitive detection, while a frequency synthesizer will produce the final microwave signal at the precise atomic resonance frequency. Detection circuitry and feedback control mechanisms, together with other signal processing techniques, will be implemented to ensure the stability and accuracy of the atomic clock. The feedback mechanism, such as a phaselocked loop or frequency modulation, will adjust the microwave signal frequency based on atomic resonance measurements. A phase-sensitive detector will be used to measure phase differences between the reference and atomic signals, enabling real-time frequency adjustments.

Finally, to enable the translation of atomic timekeeping into practical applications, a time measurement and display system will be developed. This will involve the integration of timing circuits, microcontrollers and display interfaces. Thereafter, the atomic clock will be characterized to assess key performance parameters such a stability and accuracy.

In essence, this project seeks to create a microwave-based atomic clock by investigating the fundamental atomic principles and subsystems that make up the atomic clock. Future endeavours will explore extending these techniques to cold atoms, fostering expertise in atomic timekeeping.

Speaker: Ms Shaleena Jayaram (South African Radio Astronomy Observatory)

62 Towards a high fidelity two-qubit state manipulation and readout using the ARTIQ Phaser and Grabber Modules.

T. Maddock, S. Kulmiya, S.J. Hile, D.S. Smith, S. Weidt & W. K. Hensinger

Sussex Centre for Quantum Technologies
University of Sussex
Brighton
BN1 9QH, UK

The ability to generate and distribute entanglement in open quantum systems is a prerequisite for a fully-fledged quantum computer. The former of which, within this group, has been achieved typically using geometric phase gates, with dressed states (continuous dynamical decoupling) being utilised to protect the states from dephasing noise. The use of dressing fields increases calibration and tone overhead with the number of qubits in any multiqubit gate.

Gates which utilise the J-coupling interaction, often overlooked due to inferior gate times, commute with dephasing noise operators, allowing for straightforward noise cancellation via pulsed dynamical decoupling, in addition to relaxed requirements in terms of motional decoherence [1, 2].

Recent theoretical work [1] has demonstrated an ability for faster than dispersive J coupling gates, using dynamical decoupling on each qubit; an inter-pulse delay is set such that the spectral form of this sequence drives the spin boson interaction, alleviating the main drawback suffered by this type of gate. Pulsed dynamical decoupling sequences can be engineered to ensure robustness to amplitude fluctuations, in addition to environmental noise induced decoherence.

In the regime where available Rabi frequencies are much smaller than trap frequencies, low intensity pulses must be used. In this instance, pulse shaping can be used so that, again, the spin boson interaction is driven. In light of open source STFT pulse generator gateware developed by Norman Krackow [3], pulse shaping as described in this scheme can be achieved using an integrated AWG in Artiq also known as the Phaser. We demonstrate work on the experimental implementation of this new module and its relevance towards developing fast and accurate pulse sequences to perform high fidelity trapped ion experiments.

Developing fast high speed EMCCD readout techniques will provide access to better bell state discernibility, which can be achieved in relevant timescales using Artiq's Grabber module, which offers FPGA handled EMCCD frame data via a low latency link to our Andor Solis camera. We also show the implementation of this module to enable fast readout of two-qubit states. In doing so, improved Bell state analysis can be performed within computational timescales, which will be useful for error correction and teleportation protocols.

References:

[1] : Arrazola, Iñigo, and Jorge Casanova. "Robust oscillator-mediated phase gates driven by low-intensity pulses." Communications Physics 6.1 (2023): 123.

[2]: Valahu, C. H., et al. "Robust entanglement by continuous dynamical decoupling of the J-coupling interaction." New Journal of Physics 23.11 (2021): 113012.

[3]: Kulik, Paweł, et al. "Latest developments in the Sinara open hardware ecosystem." 2022 IEEE International Conference on Quantum Computing and Engineering (QCE). IEEE, 2022.

Speaker: Tobias Maddock

63 Fabrication of ion trap microchips with advanced features for trapped ion quantum coumputing

We present the fabrication of trapped ion microchips integrated with the key features required to realise a scalable architecture for a modular microwave trapped-ion quantum computer. In our approach for ion trap quantum computing [1], high currents of up to 15 A generate large local magnetic field gradients at the ion position which, together with global microwave and RF fields, enable the implementation of high-fidelity quantum gates [2]. In order to enable such high currents within the quantum computing microchip, we fabricated surface ion trap microchips with current-carrying wires (CCWs) integrated into the silicon substrate. With the developed chips, currents up to 13 A can be applied continuously, resulting in a simulated magnetic field gradient of 144 T/m at the ion position, which is 125 μm from the trap surface. The low resistivity of the CCWs allows for a power dissipation of 1 W for 10A and 3 W for 13 A at a base temperature of 38 K for the CCWs including the compensation coils [3]. Our ion trap architecture is also modular, which means that arbitrary numbers of modules can be connected via electric fields to allow ion transport between individual modules. The key technique for this approach is aligning modules with respect to each other, requiring protruding electrodes at the edge of each module. For this purpose, silicon undercuts have also been fabricated at the edges of the developed chips. We have successfully fabricated such a chip, which has been used for coherent ion transport between two quantum computing modules [4]. We are currently working on integrating vias for inner segmented electrodes and atomic ovens.

[1] Lekitsch, Bjoern, et al. “Blueprint for a microwave trapped ion quantum

computer.” Science Advances 3.2 (2017): e1601540.

[2] Weidt, S., et al. “Trapped-ion quantum logic

[3] Siegele-Brown, Martin, et al. “Fabrication of surface ion traps with

integrated current carrying wires enabling high magnetic field gradients.”

Quantum Science and Technology 7.3 (2022): 034003.

[4] Akhtar, M., et al. “A high-fidelity quantum matter-link between ion-trap

microchip modules.” Nature Communications 14.1 (2023): 531.

Speaker: Vijay Kumar (University of Sussex)

64 Progress towards a fault tolerant microwave-driven two qubit quantum processor utilizing Bayesian statistics for state determination

We realize a universal gate-set for quantum computing with microwave nearfields
with trapped ions [1]. $^9Be^+$ ions are trapped in a surface electrode trap with
an integrated microwave electrode. Single ion addressing is done through micromotion
sidebands [2]. We approach entangling infidelity of $10^{-3}$ with Mølmer-Sørensen
gates. Based on the work done by [3] we investigate further use of Bayesian statistics
for flourescence readout and state discrimination. The state determination can be
improved by techniques to dynamically reduce readout time based on a probability
threshold. Further, we will report on utilizing belief information for each state
determination together with a time series database for post-analysis. We plan to
implement a Bayes filter on top of the time series data from our experiments to
track the experiment setup condition.
[1] C. Ospelkaus et al., Phys. Rev. Lett. 101 090502 (2008)
[2] G. Zarantonello et al., Phys. Rev. Lett. 123 260503 (2019)
[3] A. H. Myerson et al., Phys. Rev. Lett. 100 200502 (2008)

Speaker: Alexander Onkes (Institut für Quantenoptik, Leibniz Universität Hannover; PTB)

65 Trapped and cooled 88Sr+ ions in a cylindrical potential provided by a micro-fabricated ring trap

Laser-cooled trapped ions platform is one of the best candidates for the development of future quantum computing. This has generated a major worldwide research effort aimed at scaling and integrating trapping devices. As part of this effort, we are developing miniature atomic ion traps in the laboratory: Paul linear surface traps manufactured in collaboration with Nanyang Technology University and the Microelectronics Institute of Singapore. An original feature of the manufacturing process is that all the electrical contacts of the trap electrodes are made through the Silicon substrate (TSV: through silicon vias). In this way, the wire-bondings usually soldered directly to the electrodes can be offset or completely eliminated [1]. This opens the way to complex architectures, in particular cylindrically symmetrical ring traps, which cannot be made with surface connections that would break the desired symmetry.

The trapping and laser cooling of ions in cylindrically symmetrical linear Paul traps (called "ion storage rings" in their macroscopic version, diameters of around 100 mm) was demonstrated in pioneering work at Garching [2] and subsequently extended to microfabricated traps (multilayer technology) at Sandia National Labs (diameter 2.5 mm) [3] and Berkeley (diameter 95 µm) [4]. These devices are of interest because, in the absence of defects, they enable rotational symmetry for the trapped ions and thus periodic boundary conditions for the confined cold ion system (Coulomb crystal). They are also candidates for observing and manipulating the rotational quantum state of trapped ion ensembles [4].

We will present our latest results concerning the performance of TSV surface ring traps (diameters between 150 and 210 µm) manufactured in Singapore. In particular, we loaded these traps with Doppler-cooled 88Sr+ ions (from a single ion to several hundreds). Laser cooling and image acquisition enable us to estimate the defects of the trapping potential with respect to perfect rotational symmetry. The application of DC voltages to a set of segmented electrodes then makes it possible to compensate for most of these defects, which nevertheless remain the major problem to be solved in order to achieve sub milikelvin free motion.

[1]P. Zhao et al., Appl. Phys. Lett. 118, 124003 (2021).
[2]I. Waki et al.,Phys. Rev. Lett. 68, 2007 (1992).
[3]B. Tabakov et al., Phys. Rev. Applied 4, 031001 (2015).
[4] E. Urban et al., Phys. Rev. Lett. 123, 133202 (2019).

Speaker: Lilay GROS-DESORMEAUX (MPQ QITE)

66 Stopping and Trapping of Radioactive Isotopes for Precision Experiments (STRIPE)

The investigation of nuclear ground-state properties of short-lived radioactive isotopes through laser spectroscopy is an important probe of state-of-the-art nuclear-structure theories. This field has mainly been driven by Collinear Laser Spectroscopy (CLS) and Resonant Ionization Spectroscopy (RIS) in the last decades. In both techniques, the laser spectroscopy is performed in-flight which limits the interaction time between the laser and atoms to few μs. This inherently results in linewidths larger than few MHz. To increase the interaction time and with it the possible observable linewidth by orders of magnitude, a new quest has started with the goal to stop and trap radioactive isotopes for precision experiments (STRIPE). In contrast to commonly used buffer-gas filled linear Paul traps, this approach will try to circumvent the buffer gas and laser-cool the decelerated ions inside the Paul trap instead. This will enable high-precision measurements of the nuclear hyperfine structure through laser spectroscopic double-resonance experiments to investigate nuclear octupole moments. Furthermore, weak optical transitions with narrow linewidths will be explored which might open the route for investigations of King plot nonlinearities over long isotope chains. To characterize and optimize this process, a new offline beamline is currently under construction at the Institute for Nuclear and Radiation Physics of KU Leuven. This contribution will give an overview of the project and present the current status.

Speaker: Phillip Imgram (KU Leuven (BE))

67 Towards a Scalable Logical Qubit: Yb and Ba Ion Toolkit

Multi-species trapped ion quantum computing offers a promising solution to challenges around ground state cooling, optical crosstalk, and provides a natural separation between operations with contradictory requirements, particularly as the number of ions in a device is increased. We show work towards the implementation of a small logical qubit using Ytterbium (Yb) and Barium (Ba) ions in an X-junction chip trap. Our scheme uses Yb ions as data and ancilla qubits and Ba ions for cooling, with ions shuttled around between various locations on the X-junction chip as necessary for gate and measurement operations.

Preparation into the motional ground state of small ion chains can be achieved either through sideband resolved microwave pumping, or though Electromagnetic Induced Transparency (EIT) cooling applied to the Ba ions [1]. The Yb ions are sympathetically cooled by virtue of their shared motional modes, without impacting stored quantum states in the Yb ions. By encoding qubit states onto hyperfine levels of the ions ground state, we can employ microwave- and RF- driven single-qubit and multi-qubit Molmer-Sorensen (MS) quantum gates [2][3].

The application of a magnetic field gradient produces the spin motion coupling required by the MS gate, and results in separation of Zeeman levels for neighbouring ions. This frequency separation ensures low crosstalk between individually addressed single-qubit and two-qubit operations within the ion chain. Within this framework we present plans and initial progress toward the implementation of surface code fragments, compiling and optimising generic quantum circuits together with auxiliary operations for our specific scheme.

To trap Barium, we employ pulsed laser ablation (PLA) loading. A Q-switched Nd:YAG laser is being used to ablate the surface of a BaCl salt target, producing an atomized plume of neutral barium atoms, which is then ionized through resonance enhanced multi-photon ionisation (REMPI) for isotope selectivity. Additionally, we have a Ytterbium ablation target to compare the effectiveness of this method with the thermal ovens that are currently in use.

[1] Lechner, Regina, et al. ‘Electromagnetically-Induced-Transparency Ground-State Cooling of Long Ion Strings’. Physical Review A, vol. 93, no. 5, May 2016, p. 053401. DOI.org (Crossref), https://doi.org/10.1103/PhysRevA.93.053401

[2] Weidt, S., et al. "Trapped-ion quantum logic with global radiation fields." Physical Review Letters 117.22 (2016): 220501. https://doi.org/10.1103/PhysRevLett.117.220501

[3] Negnevitsky, V., Marinelli, M., Mehta, K.K. et al. Repeated multi-qubit readout and feedback with a mixed-species trapped-ion register. Nature 563, 527–531 (2018). https://doi.org/10.1038/s41586-018-0668-z

Speaker: Parsa Rahimi (University of Sussex IQT Research group)

68 Integrated photonics in trapped ion quantum computing

The integration of photonic components in surface electrode traps is a novel and impactful technology, representing a promising approach for scalable quantum computing with trapped ions [Mehta2023].
In this architecture, photonic waveguides are embedded in a trap layer underneath the electrodes to route light with high efficiency to the position of interest. Integrated gratings output the light from the chip and tightly focus it directly on the ions, creating beam spots with high intensity and the possibility of engineering the light wavefront using suitable photonic structures. Finally, this architecture can be paired with active components such as optical modulators and detectors, representing a breakthrough in integrated technologies for quantum computing.

Here we report on the last results on photonic surface traps developed at ETH Zurich. We used traps equipped with integrated waveguides and passive optical components based on silicon nitride to operate with $^{40}\text{Ca}^+$ ions. Laser beams at the wavelengths of 729, 866, and 854 nm are integrated, used to drive the qubit quadrupole transition $4S_{1/2} \to 3D_{5/2}$ and to repump the ions for cooling and spin reset, respectively. The cooling and detection light at 397 nm and the photoionization beams at 423 and 389 nm are delivered in free-space.

In this platform, we demonstrated the first two-qubit entangling gate controlled by integrated light, in a trap with one 729 integrated beam addressing multiple ions [Mehta2020].
As a next step, we demonstrated the use of integrated components to deliver spatially structured light to the ions, engineering the laser-ion interaction to the application of interest [Ricci2023]. In our design, the integrated photonic gratings are arranged to produce a passively phase-stable standing wave at the ion location. We characterized the spatial structure of the light field and the optical performance of the device using one trapped ion as a probe. Such a structured light field can be used to enhance the fidelity of quantum logical gates or metrological operations and to generate state-dependent optical potentials in a novel way.
Finally, we demonstrated for the first time the use of integrated photonics in multizone operations as a building block for scalable quantum computing [Mordini2024]. We developed techniques to mitigate the influence of the photonic structures on ion transport and implemented coherent operations between distant trap zones and simultaneous control of multiple ion qubits.
To conclude, we present an outlook of the possible research directions using integrated photonic traps on different ion species such as barium, currently in development at the University of Padua.

Speaker: Dr Carmelo Mordini (University of Padua)

69 Towards improvements in quantum networks using Fiber Fabry-Perot (FFP) microcavities

Trapped ions coupled to an optical cavity have proven to be good candidates for atom–photon interface, which provide a basis for quantum network applications. Increasing coupling strength between the cavity and ions remains a central focus for advancements of the ion-cavity systems.Promising approach involves the usage of microcavities fabricated on optical fibers.In this poster an existing experimental setup will be presented, that consists of linear Paul trap with an integrated fiber cavity along the trap axis. Additionally, the design of new MEMS surface ion traps with microactuators will be presented.

Speaker: Roberts Berkis

70 Controlling trapped-ion qubits with microwave near-fields and a stimulated-Raman laser system

Trapped-ion qubits are a promising hardware platform for quantum computing and quantum simulation. In our experiment, the qubits are encoded in two hyperfine levels of $^9$Be$^+$ ions confined in a cryogenic surface-electrode Paul trap. By integrating microwave conductors into the trap, we can generate an oscillating magnetic field and gradient at the ion’s position which can drive carrier and sideband transitions between the qubit states, respectively. In this way, motional ground state cooling, single qubit gates and entangling interactions can be implemented.
An alternative method to control the ion’s internal and motional states is the use of a stimulated-Raman laser system. For that, we generate two beams of 313 nm laser light via sum-frequency generation and subsequent second harmonic generation. To enable precise control of the frequency difference between the two beams, each beam path features a double-pass acousto-optic modulator setup with a geometry that is inherently stable with respect to thermal effects. Moreover, intensity stabilization is realized using a feedback loop with a sample-and-hold circuit.
By comparing these two methods of quantum control of trapped $^9$Be$^+$ ions, we aim to improve the performance of microwave-driven quantum gates in our setup. We will report on the status of the project and on a new generation of segmented multi-ion trap chips to be implemented in this environment.

Speaker: Emma Vandrey (Leibniz Universität Hannover)

71 Design and development optimization of X junctions for three dimensional segmented ion traps

In order to scale current hardware for trapped ion Quantum computers, it is imperative to go from the widely used one dimensional schemes (linear traps) to bi-dimensional schemes. A straightforward starting point is to implement arrays of linear traps, but they need to be efficiently connected between each other. Those interception points are called junctions, and can be X, Y or T junctions depending on the number and disposition of the incoming linear traps. In order to connect ions from different linear arrays, efficient and coherent transport across the junction is required. In this work, the design and development of X junctions via simulation is carried out using closed-loop optimization based on trap frequency and ion transport characterization.
With the aim of addressing subtle geometry variations that might lead to noticeable improvements in the junction performance, a closed-loop, feedback-driven simulation workflow is developed. Parameterized X junction designs are developed and iteratively tested by characterizing their performance for different geometric parameter sets.
The workflow was first implemented by characterizing trapping potential and ion transport through parameter sweeps. For each instance of the sweep, the optimal RF pseudo potential, which is responsible for the radial confinement within each linear trap segment, is firstly obtained. Then, the DC electrode voltages are set for each time step to maximize the transport performance across the junction is optimized.
In the following step we do not just blindly sweep through parameters, but use the transport performance results as feedback to change the set of geometric parameters towards further improvements. We also improve on the closed-loop optimization, by taking advantage of machine learning tools for reinforced learning to learn from the transport characterization results. In conclusion, our research focuses on the simulation and development of X junctions, which are crucial for the implementation of two dimensional scalable ion traps

Speaker: Santiago Emilio Bogino (Universität Mainz)

72 A Ti:Sapph laser system for the state-selective preparation of nitrogen ions

Vibrational transitions in molecules are sensitive to changes in the proton-to-electron mass ratio. In this experiment, we are using spectroscopy in a nitrogen ion clock to search for dark matter and possible time variations in the proton-to-electron mass ratio. For this, we will probe the v=0 to v=2 vibrational transition in nitrogen and look for changes in the frequency over time.
The rotational and vibrational energy levels in nitrogen are not possible to laser cool. Therefore, we must ionise nitrogen state-selectively into its v=0 state for the spectroscopy. We are able to do this using a resonance enhanced multi-photon ionisation (REMPI) scheme. We have therefore set up seeded, Fourier-limited Ti:Sapph lasers to achieve high ionisation efficiency.

Speaker: Amber Shepherd (University of Sussex)

73 Development of the antiproton trap for the GBAR experiment

The GBAR experiment aims to measure the gravitational acceleration of antihydrogen atoms within a terrestrial gravitational field. In this experiment, antihydrogen atoms are produced by the interaction of a positronium cloud with an antiproton beam. A Penning-Malmberg trap has been developed to capture antiprotons supplied by ELENA at CERN, enabling the generation of a high-intensity antiproton beam for the experiment.

Speaker: Byungchan Lee (Seoul National University (KR))

74 Phase sensitive modified cyclotron frequency measurements with single trapped antiprotons

Even though the standard model has been successful in predicting and describing subatomic phenomena, it requires symmetry under charge, particle and time inversion and can thus not explain certain cosmological observations. A difference in the fundamental properties between matter and antimatter would break CPT invariance, will further our understanding of the shortcomings of the standard model, and could potentially explain aspects of the excess of matter over antimatter. The BASE experiment is testing CPT invariance in the baryonic sector by comparing the ratios of charge-to-mass ratios and the magnetic moments of protons (p) and the antiprotons (p).

BASE uses advanced Penning-trap-systems to confine single particles inside an electrostatic potential well with a constant magnetic field [1]. By measuring the cyclotron frequencies $ω_c = q/m · B$ of a proton and an antiproton, their charge-to-mass ratio can be determined. Calculating the relative charge to mass ratio eliminates the dependence on the magnetic field and allows specifying it to a fractional precision of 16 p.p.t. [2]. By measuring the Larmor frequency ωL of both particles as well,
the g-factors $g = 2μ/μ_N = 2ω_L/ω_c$ can be specified to a fractional precision of 0.3 p.p.b. and 1.5 p.p.b. [3, 4].
$(q_{\overline{p}}/m_{\overline{p}})/(q_p/m_p) = −ω_{c,{\overline{p}}}/ω_{c,p} = −1 ± 1.6 · 10^{−11}$
$(ω_{L,{\overline{p}}}/ω_{c,{\overline{p}}})/(ω_{L,p}/ω_{c,p}) = g_{{\overline{p}}}/g_p = −1 ± 1.6 · 10^{−9}$

Since the start of the BASE experiment program, multiple improvements of the applied frequency measurement schemes have been made, decreasing the uncertainties of the measured fundamental quantities by multiple orders of magnitude. With direct frequency measurements limited by their
$T^{−1/2}$ scaling with measurement time, the next step is the implementation of phase information [5] in
the determination of the modified cyclotron frequency to reach a $T^{−1}$ scaling.

I will give an overview about BASE, the current frequency measurement schemes used, and the particular limitations and problems that we face using them. I will introduce the concept of phase sensitive frequency measurements in the context of BASE, and discuss their advantages and new
inherent precision limits.

[1] C. Smorra et al. “BASE–the baryon antibaryon symmetry experiment”. In: The European Physical Journal Special
Topics 224.16 (2015), pp. 3055–3108.
[2] M. J. Borchert et al. “A 16-parts-per-trillion measurement of the antiproton-to-proton charge–mass ratio”. In:
Nature 601.7891 (2022), pp. 53–57. doi: 10.1038/s41586-021-04203-w.
[3] Georg Schneider et al. “Double-trap measurement of the proton magnetic moment at 0.3 parts per billion precision”.
In: Science 358.6366 (2017), pp. 1081–1084.
[4] C Smorra et al. “A parts-per-billion measurement of the antiproton magnetic moment”. In: Nature 550.7676 (2017),
pp. 371–374.
[5] E. A. Cornell et al. “Mode coupling in a Penning trap: π pulses and a classical avoided crossing”. In: Phys. Rev. A
41 (1 1990), pp. 312–315. doi: 10.1103/PhysRevA.41.312.

Speaker: Philip Geissler (RIKEN (JP))

DOC-20240708-WA0002.pdf

75 Hybrid Penning-Linear-Paul trap for ion recapture in a near-zero bias magnetic trap for hydrogen/antihydrogen spectroscopy

The reason why there is no primordial antimatter in the Universe remains a mystery. Measurements with antimatter [1][2] show full compatibility with its matter counterparts at high precision and that the antimatter feels Earth's gravitational attraction similarly to matter [3] at low precision.
Antihydrogen (Hbar) is produced by trapping antiprotons and positrons in neighboring wells in a Penning-Malmberg trap and slowing mixing then. An Ioffe-Pritchard octupole magnetic trap superposed to the Penning trap allows the trapping of the produced neutral Hbars with energy below 500 mK [4]. Since trapped antiprotons and positrons are needed to create Hbars, a bias magnetic field of ~1 T is used in the trap region. This high magnetic field adds some systematic uncertainties in comparing the two-photon 1s-2s transition in H and Hbar since accurate measurements with H [5] are performed in a very low magnetic field environment. The precision of the comparison can be improved by trapping hydrogen in the same Hbar trap [6][7][8] and repeating the exact measurements with both counterparts, avoiding many systematic uncertainties such as this magnetic field effect, AC Stark shift from the same laser and enhancement cavity operation [9]. However, the strong bias magnetic field still affects the transition's lineshape and center. It is possible to ramp down the bias magnetic field and perform the 1s-2s spectroscopy with Hbar's since we can always detect the annihilation of the ionized atoms efficiently. Nevertheless, repeating the exact measurement in a near-zero bias with H is not straightforward since we can not detect the annihilation. If we keep the bias magnetic field, it is possible to recapture a fraction of the ionized H during the spectroscopy [10] by using a weak Penning trap potential, but for a near-zero magnetic field, recapturing the protons can not be accomplished.
Here, we suggest using a hybrid Penning-Linear-Paul trap, using a segmented electrode in the Penning-Malmberg trap to radially confine the ions to perform high precision 1s-2s spectroscopy in H in a near-zero field trap. We will discuss the stability of the recaptured particles in a Linear-Paul trap with a weak magnetic field along the axis, the effect of the electric field on the lifetime of the H/Hbar, lineshape of the transition, the effect of a superposed octupole field to the RF trap, patch potentials, and possible magnetic fields measurements at low fields.

[1] - Borchert et al, Nature 601, 53-57 (2022).
[2] - Ahmadi, M. et al., Nature557, 71-75 (2018)
[3] - Anderson, E.K. et al., Nature 621, 716-722 (2023)
[4] - Andresen, G. B. et al, Nature 468, 673-676 (2010)
[5] - Parthey, C. G. et al., Phys. Rev. Lett.107, 203001 (2011)
[6] - Azevedo, L.O.A. et al, Commun Phys 6, 112 (2023)
[7] - S A Jones, New J. Phys. 24 023016 (2022)
[8] - W. A. Bertsche et al 2022 J. Phys.: Conf. Ser. 2244 012080
[9] - ALPHA Collaboration, Nature Physics, Accepted - To be published
[10] - Cesar, C. L., J. Phys. B49, 074001 (2016)

Speaker: Levi Oliveira De Araujo Azevedo (Federal University of Rio de Janeiro (BR))

76 Distributed quantum sensing in noisy environments with trapped ions

Quantum sensing is a promising application of quantum technologies. The aim is to exploit the quantum nature of sensors to provide an increase in sensitivity of precision measurements. With several demonstrations of elementary quantum networks, e.g. [1, 2, 3], a natural question is whether distributed quantum sensors can provide an advantage for sensing fields with arbitrary spatial profiles. A recently published scheme [4] proposes a method of designing entangled states of distributed sensors that are robust to noise fields that are spatially distinct to the signal. This is due to being in a decoherence free subspace with respect to the noise fields. In this research, a proof-of-principle demonstration of the scheme is implemented, in which it is shown that three co-trapped entangled Ca40+ ions maintain optimal sensitivity to the strength of an artificially imprinted spatially quadratic magnetic field, in the presence of overwhelmingly noisy constant and gradient magnetic field noise sources. It is found that the prepared entangled state of the ions outperforms all unentangled estimation strategies.

[1] L. J. Stephenson et al., High-rate, high-fidelity entanglement of qubits across an elementary quantum network, Phys. Rev. Lett. 124, 110501 (2020)
[2] M. Pompili et at., Realization of a multinode quantum network of remote solid-state qubits, Science 372, 259 (2021)
[3] V. Krutyanskiy et al., A telecom-wavelength quantum repeater node based on a trapped-ion processor, arXiv:2210.05418v1 (2022)
[4] P. Sekatski et al., Optimal distributed sensing in noisy environments, Phys. Rev. Res. 2, 023052 (2020)

Speaker: James Bate (Innsbruck University)

Wednesday 10 July

Quantum Technologies

Convener: Marion Mallweger

77 Single ion dynamics in a phase-stable polarization gradient

Sisyphus cooling below the Doppler limit in polarization gradients has been a backbone of ultracold atom experiments for decades. It has recently been demonstrated for trapped ions as well. The potential advantage is that it can simultaneously cool multiple modes of a Coulomb crystal below the Doppler limit and could thus improve the time required to cool all modes of large ion crystals close to the motional ground state. So far, this has only been done using running wave polarization gradients. Localizing the ions at particular phases of the polarization gradient lowers the cooling limit by a factor of two. We demonstrate cooling in a phase-stable polarization gradient. The interferometric stability is created by splitting the light on-chip in integrated photonic waveguides and overlapping the emission from separate diffraction grating couplers. To our knowledge, this is the first experimental demonstration of the phase-dependence of polarization gradient cooling. This technique could cut down cooling times in large ion crystal quantum simulators and computers.

Speaker: Felix Knollmann

PGC_ECCTI_2024.pptx

78 Chromatic suppression of spontaneous emission

Using reflecting boundary conditions, we can control the spontaneous emission of trapped $^{138}\mathrm{Ba}^+$ ions. By reflecting the ion's fluorescence light onto itself, the single photons emitted by the ions interfere with the ions themselves, allowing control over the emission rate. The control is dependent on the solid angle at which the produced photons are retro-reflected, and in order to accomplish total control, we use a hemispherical mirror that can monitor the ion from every direction of space. When the mirror radius is tuned to achieve destructive interference at the wavelength of the produced photons, fluorescence, and hence the accompanying energy transition, can be prevented. Here, I describe our current efforts to control the decay of the $6p_{1/2}$ state of the $^{138}\mathrm{Ba}^+$ ion, which can relax by emitting 493 nm or 650 nm photons. Our goal is to demonstrate control over the decay branching ratio, which could be useful in future studies, such as suppressing an undesired relaxation branch or simplifying the energy structure of ions.

Speaker: Thomas Lafenthaler

Eccti_Thomas_Lafenthaler.pptx

79 Motional spin-locking spectroscopy

Characterization of noise of a quantum harmonic oscillator is important for many experimental platforms. We experimentally demonstrate motional spin-locking spectroscopy, a method that allows to directly measure the motional noise spectrum of a quantum harmonic oscillator. In a spin-locking experiment, the free-evolution period of a Ramsey experiment is replaced with a continuous drive of a superposition of two states. Noise leads to depolarization of the initial state with a rate of depolarization that is determined by the noise strength. Probing the transition between two motional states gives access to the motional noise spectrum. We measure motional noise of a single trapped ion in a linear Paul trap in a frequency range from 200 Hz to 5 kHz with a power spectral density that resolves noise over two orders of magnitude. Coherent modulations in the oscillation frequency of the oscillator can be probed with a fractional frequency sensitivity at the $10^{-6}$ level.

Speaker: Florian Kranzl

ECCTI_2024_Kranzl.pdf

ECCTI_2024_Kranzl.pptx

80 Multi-Channel Quantum Scattering Calculation for Ultracold Ion-Atom Collisions

We focus on the theoretical modelling of the dynamics of ion-neutral systems at ultracold temperatures (<< 1K) in order to design ways for their full quantum control. Our aims are connected to experimental investigations of alkaline earth ion - alkali atom systems with hybrid traps. Due to the laser cooling scheme a metastable d-level of the alkaline-earth ion is considerably populated in these experiments, e.g. in case of 88Sr+ ion embedded in the cloud of ultracold 87Rb atoms [1] or 138Ba+ in 6Li cloud [2]. The large internal energy of the ion induces several inelastic processes like charge-exchange, spin-orbit change collisions or electronic excitation exchange.
We compute cross sections and rate coefficients for these processes within the framework of the quantum coupled-channel model considering the fine-structure of the colliding partners and the rotational coupling. Our calculations involve potential energy curves including the determination of R-dependent spin-orbit couplings (see Figs. 1, 2) following a diabatization approach [3].
Fig.1: Selected Hund's case (a) LiBa+ potential energy curves in the molecular frame. The red shadow shows the location of an avoided crossing of 21 Σ and 31 Σ responsible of the non-radiative charge exchange (NRCE) process (red arrow): Li(2s)+Ba+(5d) → Li++Ba(6s2,1S) .
Fig.2: The R-dependent spin-orbit couplings of the first 3 dissociation limits, based on Ω=0+/-, 1, 2, 3 the projection of the total angular momentum on molecular axis.

[1] R. Ben-Shlomi, R. Vexiau, Z. Meir, T. Sikorsky, N. Akerman, M. Pinkas, O. Dulieu, R. Ozeri, Phys. Rev. A 102 ,031301(R)
[2] P. Weckesser, F. Thielemann, D. Wiater, A. Wojciechowska, L. Karpa, K.Jachymski, M. Tomza, T. Walker, T. Schaetz, Nature 600, 429 (2021)
[3] X. Xing, R. Vexiau, N. Bouloufa, O. Dulieu et al, in preparation.

We acknowledge support from the CRNS International Emerging Action (IEA) - ELKH, 2023-2024; Program Hubert Curien ”BALATON” (CampusFranceGrantNo.49848TC)–NKFIHTE ́T-FR(2023-2024)

Speaker: Tibor Jónás (HUN-REN Institute for Nuclear Research (ATOMKI), Bem tér 18/c, 4026 Debrecen, Hungary; University of Debrecen, Doctoral School of Physics, Egyetem tér 1., 4032 Debrecen, Hungary;Université Paris-Saclay, CNRS, Lab. Aimé Cotton, Bat 505, Rue du Belvédére, 91400 Orsay, France)

Tibor_Jonas_Multi_Channel.pdf

81 How universities collaborate with industry to advance quantum technologies - the role of AQT

In my talk I present some joint research projects between AQT (a company which developed as a Startup from the University of Innsbruck), research facilities and data centers. Furthermore, I explain how we aim at advancing quantum technologies by the reproducible production of certain quantum devices.

Speaker: Christine Maier (AQT)

Coffee break

eccti_coffeebreaks.pdf

eccti_coffeebreaks.pptx

Molecular Spectroscopy

Convener: Eric Endres (Universität Innsbruck)

82 Towards quantum logic spectroscopy of polyatomic molecular ions

Due to the complexity of the internal energy structure of molecular ions, control of their quantum state poses serious challenges. Contrary to atomic counterparts, most molecules lack cycling optical transitions, which prevents standard state preparation and detection techniques based on optical pumping as well as direct translational cooling schemes. These challenging problems were recently solved for some diatomic molecular ions with quantum logic spectroscopy (QLS) techniques [1, 2, 3]. Here we report on the progress in extending control capabilities of the quantum state to polyatomic molecules using co-trapped calcium ions in a new cryogenic ion-trapping apparatus.

Our approach involves the preparation of the internal molecular state with a resonance-enhanced photoionization technique [4]. Co-trapped calcium ions serve a dual purpose - sympathetically cooling translational degrees of freedom of the molecular ion and employing quantum nondemolition state detection for the molecule. Employed QLS protocol relies on the state-dependent motional excitation of molecular ions exerted by an off-resonant optical lattice [1]. The cryogenic ion-trapping setup design and the current progress in its implementation will be discussed.

The realization of the described framework opens a route to studying chemical reactions of collisions on the state-to-state level and conducting quantum logic spectroscopy with polyatomic species.

[1] M. Sinhal, Z. Meir, K. Najafian, G. Hegi, S. Willitsch, Science 2020, 367(6483), 1213.
[2] F. Wolf, Y. Wan, J. C. Heip, F. Gebert, C. Shi, P. O. Schmidt, Nature 2016, 530(7591), 457-460.
[3] C. W. Chou, C. Kurz, D. B. Hume, P. N. Plessow, D. R. Leibrandt, D. Leibfried, Nature 2017, 545(7653), 203-207.
[4] X. Tong, A. H. Winney, S. Willitsch, Physical Review Letters 2010, 105(14), 143001.

Speaker: Mikhail Popov (University of Basel)

Towards quantum logic spectroscopy of polyatomic molecular ions.pdf

83 Apparatus for deterministic ionization and loading of molecules

Our group studies the complex rovibrational structure of trapped molecular ions. These states are often inaccessible by standard quantum information readout methods, but can be explored by co-trapping them with an atomic ion for which a convenient cooling and qubit level scheme exists. The molecular states can then be coupled to an electronic state of the atomic ion via quantum logic spectroscopy. Our experiments are currently limited to investigating molecules containing Ca. In order to load arbitrary molecular species, we are building a setup where a molecular gas is leaked in, photoionized, and then axilally guided into an ion trap. We use time-of-flight mass spectrometry to map out the ion species produced from photoionization of various gasses like nitrogen or acetylene. Mass filters and ion optics will then be used to steer and focus the molecule of interest through a differential pumping region towards a linear Paul trap in a UHV chamber. Molecular ions can be injected into the trapping region through an aperture in the trap end cap, relying on interaction with a cool trapped ion string dissipate excess kinetic energy below the trapping potential.

Speaker: René Nardi (Universität Innsbruck)

84 Controlling Biomolecular Fragmentation within an Ion Funnel Interface

Analyzing biomolecular structures and spectra in the gas phase is challenging due to the large mass and intricate structures. Research frequently concentrates on selectively sampling specific biomolecules to gain insights into the broader system’s structure. This focused approach, rather than studying the entire system indiscriminately, provides valuable information about the behavior of the larger system in different environments. To conduct spectroscopic studies, an ion-trap-based setup is essential for isolating ions in the gas phase. In such an experimental arrangement, optimizing parent ion count while minimizing fragmentation is crucial.

Our recent experiments, concentrating on the impact of increased DC gradients on ion fragmentation, revealed unexpected outcomes within the ion funnel region—a site anticipated to experience significant fragmentation due to higher pressure compared to other operational regions (0.1 mbar). For this investigation, we selected deprotonated deoxyadenosine monophosphate (d-dAMP), a fundamental building block of DNA. This system has been extensively studied, and reports on collision-induced studies are already available [1]. The analysis of recorded mass spectra included evaluating the relative abundance of each fragment ion at different DC gradients by adjusting gradients across the ion funnel (GradIF) and between the ion transfer capillary (ITC) and ion funnel (GradITC). Unexpectedly, these results diverged from the anticipated correlation between higher gradients and increased fragmentation.

To understand this, we used SIMION simulations, analyzing recorded kinetic energy to determine the center-of-mass energy ($E_{cm}$). A portion of $E_{cm}$ contributed to the increment in internal energy, expressed as $E_{int}=\eta' E_{cm}$ [2], where $\eta'$ is the inelasticity parameter. The specific $\eta'$ value was obtained by fitting the energy dependence of the relative yield of a fragment ion [3]:
\begin{eqnarray}
Y(E)=Y_0\frac{(E-E_0)^n}{E},
\end{eqnarray}
where, $Y_0$, $n$, and $E_0$ serve as fitting parameters.

The simulations predicted a higher fragmentation yield in GradITC than GradIF, contrary to experimental findings. Considering fluid dynamics effects within the ion funnel, we performed Computational Fluid Dynamics (CFD) simulations using COMSOL, along with ion trajectory simulations. This confirmed the expected supersonic jet expansion at the ITC exit leading to the ion funnel. Comparing the increment in internal energy with and without CFD, CFD data aligned well with our experimental observations. While it is recognized that ions undergo collision-induced dissociation during their traversal through this device, the influence of gas flow dynamics on ion fragmentation remains unexplored.

This novel technique holds promise for future endeavors, offering a simplified simulation approach to determine the Collision-Induced Dissociation (CID) threshold of various other molecular ions.

REFERENCES

[1] Y. Ho and P. Kebarle, International journal of mass spectrometry and ion processes, vol. 165, pp. 433–455, 1997.

[2] L. Drahos and K. Vékey, Journal of mass spectrometry, vol. 36, no. 3, pp. 237–263, 2001.

[3] S. Loh, D. A. Hales, L. Lian, and P. Armentrout, The Journal of chemical physics, vol. 90, no. 10, pp. 5466–5485, 1989.

Speaker: Mrs UMA N N (PhD scholar)

85 Photodetachment spectroscopic studies of cold, trapped negative ions

Photodetachment spectroscopy is a powerful spectroscopic technique for determining the internal state distribution of a molecular anion. Previously, our group studied the threshold photodetachment spectroscopy of CN$^−$ at both 16 K and 295 K in a 22-pole ion trap and measured the electron affinity of CN with great precision (EA: 3.864(2) eV) [1]. Here we present the threshold photodetachment spectroscopy study of C$_2^−$ , speculated to exist in the interstellar medium, in a radiofrequency 16-pole ion trap at 8 Kelvin. We investigated the behaviour of the cross section near the threshold for the ground state transition, C${_2}$X ${^1}$$\Sigma{^+_g}$$ $$\leftarrow $C${_2^-}$X ${^2}$$\Sigma{^+_g}$. We measured the electron affinity of C$_2$ which is consistent with the previously measured values [3][4].
We also present the status of the absolute cross section and near threshold photodetachment spectroscopic studies of the naphthyl anion (C$_{10}$H$_7^-$), a polyaromatic hydrocarbon anion (PAH), which may also play a role in interstellar chemistry [5].

[1]. M. Simpson et al., J. Chem. Phys. 153, 184309 (2020).
[2]. M. Nötzold, R. Wild, C. Lochmann, R. Wester., Phys. Rev. A 106, 023111 (2022). ¨
[3]. K. M. Ervin and W. C. Lineberger., J. Phys. Chem. 95, 2244 (1991).
[4]. B. A. Laws, S. T. Gibson, B. R. Lewis, R. W. Field., Nat. Commun. 10, 1(2019).
[5]. M. L. Weichman J. B. Kim, J. A. Devine, D. S. Levine, D. M. Neumark J. Am. Chem. S 137,4 (2015).

Speaker: Sruthi Purushu Melath

Lunch break

Lab tours

Quantum Information & Computing

Convener: Gabriel Araneda

86 Deterministic Quantum Gate Teleportation across a Trapped-Ion Quantum Network

Quantum gate teleportation utilises shared entanglement and local operations and classical communication to mediate logical gate operations between qubits that cannot directly interact, making it an essential tool for the modular quantum computing architecture [1]. In this work, we demonstrate the deterministic teleportation of a controlled-Z gate between two ${}^{43}\textrm{Ca}^+$ hyperfine clock qubits located in separated trapped-ion quantum processors, measuring an average gate fidelity of 86.2(8) %. We achieve this by combining state-of-the-art remote entanglement between two ${}^{88}\textrm{Sr}^+$ network ions [2] and local mixed-species entangling gates to mediate an interaction between co-trapped ${}^{43}\textrm{Ca}^+$ memory ions [3]. We discuss how this system enables distribution of a circuit comprising multiple instances of gate teleportation across our quantum network. Our results pave the way for distributed quantum computation based on networks of trapped-ion quantum processors.

[1] D. Gottesman, I. Chuang, Demonstrating the viability of universal quantum computation using teleportation and single-qubit operations. Nature 402, 390–393 (1999).

[2] L. Stephenson, D. Nadlinger, B. Nichol, S. An, P. Drmota, T. Ballance, K. Thirumalai, J. Goodwin, D. Lucas, and C. Ballance, High-Rate, High-Fidelity Entanglement of Qubits Across an Elementary Quantum Network, Physical Review Letters 124, 110501 (2020).

[3] P. Drmota, D. Main, D. Nadlinger, B. Nichol, M. Weber, E. Ainley, A. Agrawal, R. Srinivas, G. Araneda, C. Ballance, and D. Lucas, Robust Quantum Memory in a Trapped-Ion Quantum Network Node, Physical Review Letters 130, 090803 (2023).

Speaker: Dougal Main (University of Oxford)

Distributed Quantum Computing - ECCTI Talk.pdf

87 Realization a phononic network with collective modes in trapped ion system

A network of bosons evolving among different modes while passing through beam splitters and phase shifters has been applied to demonstrate quantum computational advantage. Such networks have mostly been implemented in optical systems using photons. However, technical bottlenecks exist in photon systems. In particular, photon loss and non-deterministic generation and inefficient detection of photonic states hinder their further scalability and the demonstration of quantum advantage. It thus becomes desirable to explore new experimental platforms.
Quantized excitations of vibrational modes (phonons) of trapped ions are a promising candidate to realize such bosonic networks. Here, we demonstrate a minimal-loss programmable phononic network in which any phononic state can be deterministically prepared and detected[1]. We realize networks with up to four collective vibrational modes, which can be extended to reveal quantum advantage. This network has the capability that couple the ions with vibration modes to prepare, interfere, and measure phonons distributed in different modes, which achieves the ability to act as a boson sampling platform.
We experimentally demonstrate that phonons can be deterministically prepared and detected and that the number of phonons is nearly conserved while propagating in the network. By programmable operations throughout the boson sampling experiment, our system has demonstrated the ability to implement bosonic algorithms with high fidelity. We benchmark the performance of the network for an exemplary tomography algorithm using arbitrary multi-mode states with fixed total phonon number. We obtain high reconstruction fidelities for both single- and two-phonon states. Our experiment demonstrates a clear pathway to scale up a phononic network for quantum information processing beyond the limitations of classical and photonic systems.
Furthermore, we explore the possibility of realizing fault-tolerant quantum computation with error mitigation scheme, which can be realized with current system scale and fidelity. Based on quantum channel purification method, we are able to suppress all kinds of incoherent noise in unitary phonon operations. Our research will promote the development of quantum error mitigation in the spin-phonon hybrid system in ion trap, and provide a reference for the implementation of large-scale bosonic algorithms.

[1] Chen, W., Lu, Y., Zhang, S., Zhang, K., Huang, G., Qiao, M., ... & Kim, K. (2023). Scalable and programmable phononic network with trapped ions. Nature Physics, 19(6), 877-883.

Speaker: Dr Wentao Chen (Tsinghua University)

Realization of a phononic network with collective modes in trapped ion system .pdf

88 An ion trap quantum processor with integrated ion-photon interface

The aim of this project is to build a quantum computing processor with integrated ion-photon interface. It consists of an ion trap with zones for ion loading, QIP and a zone with an integrated optical cavity for enhanced communication. The electrode structure is designed for dual species operation, ion swapping and ion chain splitting. To achieve highly efficient high-fidelity quantum communication between processors, the system is equipped with an integrated cavity, strongly coupling to the trapped ion. To realize this, we designed a chip, which was manufactured using femtosecond laser induced selective etching (FLISE) from a fused silica substrate, and subsequently gold coated. Employing trenches between the electrodes the chip can be metalised without masks. The cavity is formed of fused silica rods instead of optical fibres as has been used previously [1] in order to improve the photon collection efficiency. In previous works, researchers have reported effective photonic entanglement by using high-numerical-aperture lens’ to couple two ions’ qubits into single-mode optical fibres to attain high rate and fidelity [2]. For our system, we expect significantly higher entanglement rates with high fidelity due to strong coupling operation.

[1] H. Takahashi et al., Phys. Rev. Lett., vol. 124, p. 013602, (2020).
[2] L. J. Stephenson et al., Phys. Rev. Lett., vol. 124, p. 110501, (2020).

Speaker: Maoling Chu (University of Sussex)

2024ECCTI-Maoling.pptx

89 Setting up a high performance quantum computing experiment with trapped Barium ions

Our project aims at setting up an ion-trap based, high-performance quantum computer, to push the current limits of gate fidelities and SPAM errors. We want to achieve such by using Barium as our qubit platform, which offers some key advantages over its most prominent competitors Calcium and Ytterbium. One example are the laser wavelengths required to interact with Barium, which are suited for integrated optics, further enhancing scalability and future on-chip implementations. The long lifetime of its optical qubit leads to a longer T1 time by more than an order of magnitude. The low-field optical clock qubit in one of Bariums isotopes, as well as the possibility of using hyperfine ground-state qubits push T2 times by about two orders of magnitude when compared to similar transitions in Calcium 40.

The heart of our setup is a standard Paul trap. It is situated inside a titanium vacuum chamber. The decision to move from stainless steel to titanium was made, as the rate of hydrogen outgassing for titanium is more than a factor of 10 smaller, which should also result in a correlating decrease in achievable pressure. A first characterisation of the setup via collision rates of the ions, which was measured to be 0,00029(1) /ion/minute, about a magnitude lower than what can be found in other room temperature ion traps in our laboratory, confirmed as much.

One big positive of using Barium is the long lifetime of its D5/2 state, which is commonly used for optical qubits, or for readout. With 30 seconds, it is more than an order of magnitude longer than in Calcium, and more than three compared to Ytterbium. Due to this, combined with the higher detection efficiency due to the higher quantum efficiency of EMCCD cameras at 493 nm rather than 397, or 370 nm, and a high numerical aperture in our setup of 0.6, one can reach much higher readout fidelities. Though we are not yet able to prepare states with high purity, or perform gates, first measurements allow us to estimate the readout error in our setup to be at, or just below 10^-5.

The next steps, before we can start measuring coherence times and testing different gate schemes, is to optimise state preparation. For Barium 137, an isotope with non-zero nuclear spin, there are new techniques, for example by incorporating a microwave, that allow error rates as low as 1.1*10^-5. The long-term goal of the project is to push the current limit of single qubit, and entangling gates. To achieve such, we will make use of single qubit Raman gates between hyperfine ground-states at 532 nm on the one hand, and new entangling gate schemes, such as transversal gradient gates or counterpropagating light-shift gates, as well as more established ones such as Mølmer– Sørensen style gates, also with Raman transitions at 532 nm. The calculated infidelities, given the known experimental parameters in our setup, are in the low 10^-5 for single qubit, and 10^-4 for entangling gates.

Speaker: Lorenz Panzl (Universität Innsbruck)

presentation_Panzl.pdf

presentation_Panzl.pptx

90 Quantum information processing with metastable states in trapped barium ions

Trapped $^{137}\textrm{Ba}^+$ ions possess two long-lived hyperfine manifolds in which quantum information can be stored: the ground $S_{1/2}$ level and the metastable $D_{5/2}$ level. The metastable level does not couple to the fluorescence beams, so information stored there is protected during dissipative operations such as cooling, state preparation or readout. This allows for these operations to be performed mid-circuit, a requirement for most error correction schemes. In addition, gates can be driven via two-photon Raman transitions using light at 532 nm in both levels, simplifying experimental setups.

Here, we present a system for quantum computation experiments with chains of $^{137}\textrm{Ba}^+$. A fibre network coupled to a novel photonic chip is used to generate an array of 532 nm beams that are individually focused on each of the ions. This enables the implementation of all logical and dissipative operations on a target subset of qubits. Furthermore, the ions are stored in a microfabricated linear trap with a segmented electrode structure [1] that can generate complex DC potentials. This allows us to modify the axial position of the ions to match the addressing beam array, as well as rotate the direction of the crystal's radial modes of motion to optimise high-fidelity two-qubit operations.

Additionally, we use the system and our control of the ground and metastable levels to implement a novel state-preparation and measurement (SPAM) protocol based on the detection of population leakages. We achieve SPAM infidelities as low as $5 \times 10^{-6}$, the lowest reported. We also discuss how information processing using multi-dimensional quantum systems could be implemented in this system.

[1] K. Choonee, G. Wilpers and A. G. Sinclair, doi: 10.1109/TRANSDUCERS.2017.7994124.

Speaker: Andres Vazquez Brennan (University of Oxford)

AVB_ECCTI_2024.pdf

AVB_ECCTI_2024.pptx

Coffee break

eccti_coffeebreaks.pdf

eccti_coffeebreaks.pptx

Skill session: Critical thinking for constructive conversations by Jean-luc Doumont

Thursday 11 July

Nuclear Physics

Convener: Phillip Imgram (KU Leuven (BE))

91 Status and Further Development of the Single Ion Penning Trap (SIPT) Mass Spectrometer

Precision mass measurements are necessary in almost all aspects of nuclear physics, including nuclear structure, nuclear astrophysics, and fundamental symmetries. Currently, the Low Energy Beam and Ion Trapping (LEBIT) facility employs two well-established techniques: Time-of-Flight Ion Cyclotron Resonance (TOF-ICR) and Phase-Imaging Ion Cyclotron Resonance (PI-ICR). While these two techniques perform well for precision measurements, the drawback is that they require tens to hundreds of ions to produce the measurement. With the Facility for Rare Isotope Beams (FRIB) now online, new rare isotopes are being produced, albeit at very low rates. In order to best use these rates, a different measurement technique called Fourier-Transform Ion Cyclotron Resonance (FT-ICR) is to be used in the Single Ion Penning Trap (SIPT) system. This technique is non-destructive and can theoretically be done with one ion. The system was commissioned, and general studies were produced, including a proof of concept measurement of Rb85+. From these studies, there is a clear path forward for further hardware development to improve the sensitivity of the system. Additionally, progress has been made with using machine learning algorithms to aid with the analysis process. The recent progress will be reviewed, and the path forward for SIPT will be discussed.

Speaker: Hannah Erington (Facility for Rare Isotope Beams (Michigan State University))

Erington-ECCTI.pdf

92 The stacked-ring ion guide and MR-ToF MS developed for the NEXT experiment

The NEXT experiment [1] is currently being built at the AGOR facility in Groningen. NEXT aims to study Neutron-rich EXotic, heavy nuclei around N=126 and in the transfermium region which are produced in multinucleon Transfer reactions. Precision mass spectrometry and decay spectroscopy will be used to characterize these nuclei.

The target-like transfer products are pre-separated from the primary beam and lighter projectile-like products within the magnetic field of a superconducting solenoid magnet. They are slowed down by use of a gas catcher. A continuous and divergent beam of low energy ions extracted from the gas catcher has to be transformed to well-focused bunches of ions with keV energy suitable for time-of-flight mass measurements. For this purpose a new ion guide consisting of a stack of ring electrodes has been developed [2]. A recently designed multi-reflection time-of-flight mass spectrometer (MR-ToF MS) [3] will be used for isobaric separation and mass measurements.

At the moment, the custom-made ion guide and MR-ToF MS are being commissioned and their performance are being studied using an alkali ion source. In this talk, the first tests of the setup will be presented and discussed.

[1] J. Even, X. Chen, A. Soylu, P. Fischer, A. Karpov, V. Saiko, J. Saren, M. Schlaich, T. Schlathölter, L.
Schweikhard, J. Uusitalo, and F. Wienholtz, The NEXT Project: Towards Production and Investigation of Neutron-Rich Heavy Nuclides, Atoms 10, 59 (2022).
[2] X. Chen, J. Even, P. Fischer, M. Schlaich, T. Schlathölter, L. Schweikhard, and A. Soylu, Stacked-Ring Ion Guide for Cooling and Bunching Rare Isotopes, Int. J. Mass Spectrom. 477, 116856 (2022).
[3] M. Schlaich, J. Fischer, P. Fischer, C. Klink, A. Obertelli, A. Schmidt, L. Schweikhard and F. Wienholtz, A multi-reflection time-of-flight mass spectrometer for the offline ion source of the PUMA experiment, Int. J. Mass Spectrom, 495, 117166 (2024).

Speaker: Marko Brajkovic (University of Groningen, the Netherlands)

Brajković Marko.pptx

93 MIRACLS: Laser spectroscopy of radioactive isotopes in an MR-ToF device

A host of techniques have been developed to study the nuclear properties of exotic isotopes produced at radioactive ion beam (RIB) facilities. One such technique is collinear laser spectroscopy (CLS), which provides a nuclear model-independent way of extracting observables such as nuclear charge radii, electromagnetic moments, and spins from the hyperfine spectrum of a particular atomic species.

The Multi Ion Reflection Apparatus for CLS (MIRACLS) is a new experimental setup in the ISOLDE RIB facility at CERN which aims to improve the sensitivity of conventional CLS by conducting it in a high-energy (> 10 keV) multi-reflection time-of-flight (MR-ToF) device [1, 2]. This type of ion trap utilizes two electrostatic mirrors to reflect ion bunches back and forth for several thousands of revolutions. In this configuration, we gain a sensitivity boost compared to conventional CLS since ion bunches are “recycled” after each revolution. As a result, exotic radionuclides with very low production yields become accessible, such as the magnesium isotope $^{34}$Mg, which will be the first physics case of MIRACLS and will give fresh insights on the so-called “island of inversion” around $^{32}$Mg.

Besides CLS, the high-energy MR-ToF device at MIRACLS can also be used for highly selective, high-flux mass separation to provide purified beams of radioactive isotopes [3]. These pure beams are a requirement for other experimental programs such as PUMA, which aims to exploit antiprotons to probe the surface effects of atomic nuclei such as halo nucleons or neutron skins [4].

This contribution will describe the operating principles of the Paul trap for ion beam preparation and the MR-ToF device at MIRACLS, discuss the latest commissioning results of the MIRACLS experiment, and give an outlook to the planned measurement of the charge radius of $^{34}$Mg.

References
[1] Simon Sels et al. “First steps in the development of the multi ion reflection apparatus for collinear laser spectroscopy”. In: NIMA B 463 (2020), pp.310-314.
[2] F.M. Maier et al. “Simulation studies of a 30-keV MR-ToF device for highly sensitive collinear laser spectroscopy”. In: NIMA A 1048 (2023).
[3] F.M. Maier et al. “Increased beam energy as a pathway towards a highly selective and high-flux MR-ToF mass separator”. In: NIMA A 1056 (2023).
[4] T Aumann et al. “PUMA, antiProton unstable matter annihilation". In: Eur. Phys. J. A 58.5 (2022), p. 88.

Speaker: Anthony Roitman (McGill University, (CA))

miracls-animation.mp4

presentation.pdf

94 Probing the nuclear magnetic octupole moment of trapped Sr ions

At the Institute for Nuclear and Radiation Physics of KU Leuven (IKS) we started a project to measure data on the magnetic octupole moment ($\Omega$) of single valence radioactive nuclei. While currently this observable has only scarcely been measured, and is thus poorly understood, preliminary shell model and Density functional theory (DFT) calculations indicate $\Omega$ may display a strong sensitivity to nuclear shell effects, even stronger than the dipole moment. It may also be well suited to probe the distribution of neutrons within the nucleus, and study fundamental properties of nucleons of stable and radioactive isotopes. This objective presents several challenges, both technical and scientific, as there are presently no methods that reach the precision required to measure $\Omega$ for short-lived isotopes of any element. In this context, the first study will be performed on the stable $^{87}Sr^+$. With 49 neutrons, $^{87}Sr^+$ is characterized by a single hole in the N=50 closed shell, which makes it more easily compared with a variety of theoretical calculations. Once measurements with $^{87}Sr$ are demonstrated, it could be possible to extend them to the long-lived $^{83,85,89}Sr^+$ here at IKS. A non-zero $\Omega$ leads to small energy shift of the hyperfine structure. We aim to measure these splitting with a precision of the order of 1-10 Hz on the hyperfine intervals, which should result in a measurement of $\Omega$ with a precision of 10$\%$. This has been demonstrated feasible with stable
$^{137}Ba^+$, homologue of $Sr^+$, inside ion traps [1]. This contribution aims to offer a broad understanding of the project and present the latest developments in the laboratory.

References
[1] N. C. Lewty, B. L. Chuah, R. Cazan, B. K. Sahoo, and M. D. Barrett, “Spectroscopy
on a single trapped 137ba+ ion for nuclear magnetic octupole moment determination,”
Optics Express, Sep. 10, 2012. doi: 10.1364/OE.20.021379.

Speaker: Pierre Lassegues (KU Leuven (BE))

ECCTI Probing the nuclear magnetic octupole moment of.pdf

Coffee break

eccti_coffeebreaks.pdf

eccti_coffeebreaks.pptx

Precision Spectroscopy & Atomic Clocks

Convener: Markus Wiesinger (Ludwig Maximilians Universität (DE))

95 New physics searches with highly charged ions

Highly charged ions (HCI) are promising candidates for novel optical clocks with applications in frequency metrology and tests of fundamental physics [1]. Typically, megakelvin-range temperatures needed to produce HCI hinder high-precision spectroscopy. To overcome this, we extract HCI from an electron beam ion trap (EBIT) and transfer them to a cryogenic linear Paul trap. There, single HCI are sympathetically cooled by laser-cooled Be$^{+}$ ions down to millikelvin temperatures, thus enabling quantum logic state readout [2]. We demonstrated in this way an optical clock based on Ar$^{13+}$, and determined its absolute frequency with sub-Hz uncertainty [3] against the Yb$^+$ octupole ion clock at PTB [4]. Our techniques are readily applicable to many ions, e. g. Ca$^{14+}$ [5] as well as Xe HCI [6]. Recently, we determined the isotope shift of a narrow M1 transition in stable even isotopes of Ca$^{14+}$ with 150 mHz accuracy. We combine these results with available isotope-shift data of Ca$^+$ [7] in a King plot which is sensitive to a new force that would couple electrons and neutrons [8,9]. In this way, we strengthen the constraints on the existence of such a hypothetical interaction by a factor of about five as compared to previous studies [7]. We also estimate how far improved measurements of Ca isotope masses and isotope shifts of the Ca$^+$ S$_{1/2}$ - D$_{5/2}$ transition would enhance such constraints.

[1] M. Kozlov, et al., Rev. Mod. Phys., 90, 045005 (2018)
[2] P. Micke, T. Leopold, S.A. King et al., Nature 578 (2020)
[3] S. A. King, L. J. Spiess, et al., Nature 611, 43 (2022)
[4] R. Lange et al., Phys. Rev. Lett. 126, 011102 (2021)
[5] N. Rehbehn, et al., Phys. Rev. A 103, L040801 (2021)
[6] N. Rehbehn, et al., Phys. Rev. Lett. 131, 161803 (2023)
[7] T. T. Chang et al., arXiv:2311.17337v1, 123003 (2023)
[8] J. C. Berengut, et al., Phys. Rev. Lett. 120, 091801 (2018)
[9] J. C. Berengut, et al., Phys. Rev. Research 2 043444 (2020)

Speaker: Alexander Wilzewski

AW_ECCTI_2024.pdf

AW_ECCTI_2024.pptx

96 Towards XUV Frequency Comb Spectroscopy of Trapped He+ Ions

The energy levels of hydrogen-like atoms and ions are accurately described by bound-state quantum electrodynamics (QED). The frequency of the narrow 1S-2S transition of atomic hydrogen has been measured with a relative uncertainty of less than $10^{-14}$. In combination with other spectroscopic measurements of hydrogen and hydrogen-like atoms, the Rydberg constant and the proton charge radius can be determined. The comparison of the physical constants obtained from different combinations of measurements serves as a consistency check for the theory [1]. For QED tests, it is also interesting to measure hydrogen-like systems other than hydrogen, which are more sensitive to different terms of the theory. The measurement of the Lamb shift in muonic hydrogen, for instance, gave rise to the proton radius puzzle [2].
Another interesting spectroscopic target is the hydrogen-like He$^{+}$ ion. Ideal conditions for high-precision measurements can be achieved, since the He$^+$ ions can be held nearly motionless in the field-free environment of a Paul trap. Interesting higher-order QED corrections scale with large exponents of the nuclear charge, making this measurement much more sensitive to these corrections compared to hydrogen.
In this talk, we describe our progress towards precision spectroscopy of the 1S-2S two-photon transition in He$^{+}$ [3]. The transition can be directly excited by an extreme-ultraviolet frequency comb at 60.8 nm generated by a high-power infrared frequency comb using high-harmonic generation (HHG). The spectroscopic target is a small number of He$^{+}$ ions trapped in a linear Paul trap and sympathetically cooled by co-trapped Be$^{+}$ ions. After successful excitation to the 2S state, a significant fraction of the He$^{+}$ ions will be further ionized to He$^{2+}$ and remain in the Paul trap. Sensitive mass spectrometry using secular excitation will reveal the number of trapped He$^{2+}$ ions and will serve as a single-event sensitive spectroscopy signal. In order to perform Doppler-free spectroscopy, the frequency comb is split into counterpropagating double pulses which are overlapped at the ions. Possible signals to test and optimize the pulse-overlap are two-photon dissociation processes of BeH$^{+}$ using 204 nm and 255 nm light, which are generated as the 5th and 4th harmonic of the infrared frequency comb, respectively.

[1] T. Udem Nature Phys 14, 632 (2018)
[2] R. Pohl et al. Nature 466, 213 (2010)
[3] J. Moreno et al. Eur. Phys. J. D 77, 67 (2023)

Speaker: Florian Egli (Max Planck Institute of Quantum Optics)

ECCTI_2024_Egli.pptx

97 Transportable optical clock for remote comparisons

We report on a transportable and user-friendly optical clock that uses the electric quadrupole transition ($\phantom{}^2S_{1/2}-\phantom{}^2D_{3/2}$) of a single trapped $\phantom{}^{171}$Yb$^+$ ion at 436~nm as the reference. The clock has been developed in an industry-lead collaboration (Opticlock) and is set up in two 19" racks. The main advantages of the system are its ability to robustly operate continuously over weeks and that it provides transportability. As a first step towards remote comparisons, Opticlock will travel to Finland in August 2024 to be compared with the $\phantom{}^{88}$Sr$^+$ clock at VTT MIKES. For this proof of concept campaign, Opticlock is aimed to demonstrate a short-term frequency instability below $5\times10^{-15}\sqrt{\tau}$ and a systematic uncertainty below $5\times10^{-18}$. The frequency instability of Opticlock has been improved by reducing the dead time required for magnetic field decay and its systematic uncertainty reduced by direct measurements of AC magnetic field and improved knowledge of the shift resulting from thermal radiation. Furthermore, a frequency comb generator is set up and integrated into the system. Prior to the remote measurement, the optical clock performance is assessed by local test transportation that identifies weak links in the system. The results pave the way for future key comparisons of high-performance optical clocks using transportable standards as an alternative to satellite-based techniques and optical fiber links.

Speaker: Mr Saaswath J. K.

Lunch break

Lab tours

Quantum Simulation

Convener: Marco Valentini (Universität Innsbruck)

98 Entanglement generation in 2D ion crystals

Quantum simulation is an approach to investigate a complex quantum system of interest by mimicking it with another, well-controllable and measurable system. One of the platforms that suitable for the task is trapped ions, held either in the form of a lattice in a Penning trap or as a linear chain in a Paul trap. The former can trap many more ions, while the latter has the important advantage of having site-resolved control and readout of individual ions’ electronic states. In our project we aim to overcome the limitations of a standard Paul trap and go beyond 1D chains, expanding ion crystals to 2D lattice while keeping individual addressing and readout. To do so, we have designed and built a monolithic Paul trap, capable of storing 100+ ions in a stationary 2D crystal. To create multiparticle entanglement in the system, state-dependent forces are induced via Raman transition within the ground state manifold of 40Ca⁺ ion. These forces make out-of-plane (drumhead) modes of a 2D crystal act as an entanglement mediator, bringing ions to a complex multiparticle state. We implemented Ising, transverse field Ising and XX spin-spin interaction models on our experimental setup, that led to creation of highly entangled collective spin state of up to 91 particles with a measurement variance below the standard quantum limit, also known as a spin-squeezed state. These states potentially provide an advantage in spectroscopy precision over classical states. Furthermore, improvements on search for optimal interaction parameters and achievable metrological gain given by variational quantum-classical approach were studied.

Speaker: Artem Zhdanov

ECCTI 2024.pptx

99 Optical tweezer optimisation for trapped-ion quantum simulation

Trapped ion crystals offer a natural platform for quantum simulations. They provide advantageous conditions such as long coherence times and organization into lattice crystalline structures with fully connected interactions[1-2]. With this setup one can engineer spin-Hamiltonians whose interactions are mediated by the crystal’s phonon modes[3-6]. Our novel approach adds optical tweezers, i.e. tightly focused laser light, which is used to manipulate the ion crystals’ sound-wave spectra. This allows extra tunability over the ion interactions, paving the way to the simulation of a wide range of spin-Hamiltonians[7-9]. We show experimental work on a trapped-ion tweezer setup, detailing a tweezer optimization routine and alignment on the ions. We characterize the beam profile and observe tweezer-dressing of the ion states[10].

[1] Wang, P. et al., Nat Commun 12, 233 (2021).
[2] R. Blatt, D. Wineland, Nature 453, 1008-15 (2008).
[3] A. Bermudez et al., Phys. Rev. Lett. 107, 207209 (2011).
[4] H. Kaufmann et al., Phys. Rev. Lett. 109, 263003 (2012).
[5] P. Richerme, Phys. Rev. A 94, 032320 (2016).
[6] R. Nath et al., New J. Phys. 17, 065018 (2015).
[7] J.D.Espinoza et al., Phys. Rev. A 104, 013302 (2021).
[8] M. Mazzanti et al., Phys. Rev. Lett. 127, 260502 (2021).
[9] L.Bond et al., Phys. Rev. A 106, 042612 (2022).
[10] M. Mazzanti et al., in preparation.

Speaker: Maria Clara Robalo Pereira (University of Amsterdam)

Optical tweezer optimisation for trapped-ion quantum simulation

100 Investigating interference with phononic bright and dark states in a trapped ion

Interference underpins some of the most unusual and impactful properties of both the classical and quantum worlds, from macroscopic systems down to the level of single photons. In this work a new description of interference, based on the formation of collective bright and dark states, is investigated experimentally. We employ a single trapped ion, whose electronic states are coupled to two of its motional modes in order to simulate a multi-mode light-matter interaction. We observe the emergence of phononic bright and dark states for both a single phonon and a superposition of coherent states. The collective dynamics of these systems demonstrate that a description of interference based solely on bright and dark states is sufficient to explain the light-matter coupling of any initial state in both the quantum and classical regimes.

Speaker: Robin Thomm

ECCTI Robin.pdf

ECCTI Robin.pptx

Quantum Information & Computing

Convener: Marco Valentini (Universität Innsbruck)

101 Scaling of micro-fabricated Penning ion traps

We present the design and industrial fabrication of a micro-penning trap.

To fully harness the potential of trapped ions for applications in quantum information processing, it is necessary to scale to large numbers of ions. By building upon existing technologies in micro-fabrication, surface-electrode traps provide a promising approach for a scalable architecture. However, the conventional surface-electrode Paul trap, which relies on strong radio frequency (RF) fields for ion confinement, suffers from limitations such as heat dissipation and restricted connectivity. The recent demonstration of a micro-fabricated surface-electrode Penning trap presents a promising alternative [1]. Penning traps, which operate with a strong, homogeneous magnetic field, eliminate the need for strong RF fields and offer improved ion positioning and connectivity in a three-dimensional trapping region [2].

We present the design of the next generation in micro-fabricated Penning traps, designed for trapping a two-dimensional array of beryllium ions. The trap is split into two zones, a loading zone and a working zone. The loading zone is optimized for creating a deep trapping potential. After an ion is initially trapped in the the loading zone, it is transported into the working zone, where several ions can be brought into close vicinity of each other to perform entangling operations. The design features a planarized multi-metal layer stack on a silicon substrate. The trap is being fabricated in the industrial cleanroom facilities of Infineon Technologies Austria AG in Villach. At the time of writing, the fabrication is ongoing. In the first experiments, we will investigate the transport from the loading zone into the working zone as well as the interaction between ions trapped in separate wells of the trap potential. With these and further experiments, we hope to examine the capabilities of micro-fabricated Penning traps as an alternative to segmented Paul traps in architectures like Quantum CCD.

[1] S. Jain et al. “Unit cell of a Penning micro-trap quantum processor”.
In: (Aug. 2023). DOI: 10.48550/ARXIV. 2308.07672. arXiv: 2308.07672 [quant-ph].

[2] S. Jain et al. “Scalable Arrays of Micro-Penning Traps for Quantum Computing and Simulation”. In: Phys. Rev. X 10 (3 Aug. 2020), p. 031027. DOI: 10.1103/PhysRevX.10.031027. URL: https://link.aps.org/doi/10. 1103/PhysRevX.10.031027.

Speaker: Kilian Hanke (ETH Zurich, Infineon Technologies Austria)

2024-07-07_Kilian_Hanke_Scaling of Micro-Fabricated Penning Ion Traps v1.pptx

102 Overcoming and harnessing non-commuting dynamics in trapped ions

A trapped ion forms a hybrid system consisting of the electronic spin and bosonic motional modes. The Hamiltonian describing the interaction between laser light and this hybrid system, when containing only commuting terms, leads to simple dynamics. However, the presence of non-commuting terms, either due to spurious off-resonant interactions or deliberate inclusion, leads to complex and rich dynamics. We present two regimes for dealing with this complexity: either by suppressing the unintended non-commuting terms and recovering simpler dynamics or by harnessing the rich dynamics to realize previously experimentally unexplored interactions.

In the first regime, an off-resonant non-commuting term present in Mølmer–Sørensen two-qubit entangling gates causes an error that increases with the drive strength. This manifests as an effective speed limit of two-qubit entanglement via this method. However, using phase stabilized standing waves, we can suppress this non-commuting term and break this speed limit [Saner, Bazavan et al. 2023].

In the second regime, we generate non-linear bosonic interactions by combining non-commuting spin-motion couplings [Sutherland et al. 2021]. Using two interactions linear in the bosonic mode with non-commuting spin conditioning, we generate effective non-linear interactions with more favourable scaling than conventional techniques driving higher order sidebands [Meekhof et al. 1996]. To maintain the non-commuting relationship between the spin-components, we actively stabilize the optical phase of the driving fields. As such, we are able to demonstrate nth order non-linear interactions: squeezing, trisqueezing, and quadsqueezing [Bazavan et al. 2024], the latter of which we believe is the first experimental demonstration.

The common underlying physics, involving non-commuting terms, and the experimental requirements, such as the active stabilization of the optical phase in the driving fields, allow for the utilization and concurrent optimization of the same experimental apparatus, which we shall discuss.

1. Saner, S., Bazavan, O. et al. Breaking the Entangling Gate Speed Limit for Trapped-Ion Qubits Using a Phase-Stable Standing Wave. Phys. Rev. Lett. 131, 220601 (2023).
2. Sutherland, R. T. & Srinivas, R. Universal hybrid quantum computing in trapped ions. Phys. Rev. A 104, 032609 (2021).
3. Meekhof, D. M., Monroe, C., King, B. E., Itano, W. M. & Wineland, D. J. Generation of Nonclassical Motional States of a Trapped Atom. Phys. Rev. Lett. 76, 1796–1799 (1996).
4. Băzăvan, O. et al. Squeezing, trisqueezing, and quadsqueezing in a spin-oscillator system. Preprint at http://arxiv.org/abs/2403.05471 (2024).

Speaker: Donovan Webb (University of Oxford)

ECCTI_2024_DW_0704.pptx

Coffee break

eccti_coffeebreaks.pdf

eccti_coffeebreaks.pptx

Skill session: Colloquium by Rainer Blatt

Conference dinner

Friday 12 July

Antimatter

Convener: Danielle Louise Hodgkinson (University of California Berkeley (US))

103 Adaptable platform for trapped cold electrons, hydrogen and lithium anions and cations

Cold-charged particles play an essential role in interstellar molecular formation, are present in many high-precision experiments, antimatter physics, and chemistry, and are also relevant for studies on the origin of biological homochirality. In this contribution, I will describe a system based on the Matrix Isolation Sublimation (MISu) technique [1],[2] to generate and trap these species in the laboratory. After growing a thin film of Neon upon a cold (4 K) sapphire subtract, we implant different species inside this film via laser ablation of a solid target. With a heat pulse to the sapphire surface, we sublimate the solid neon at low temperatures, and the inert gas carries the particles that were confined inside the solid, producing a beam at low energies. We guide the charged particles using the magnetic field produced by two perpendicular coils and trap the particles in a Penning-Malmberg trap using low voltages (~1 V) and weak magnetic fields (~0.1 T).
We have measured energy distribution for positive and negative trapped charge particles whose peak was below 25 meV. Using an on-trap-time-of-flight scheme, we demonstrate the presence of electrons, hydrogen anions, protons, lithium cations and anions, and light molecular ions.
The hydrogen anions can be used to produce a cold sample of neutral trappable hydrogen by near-threshold photodetachment (0.754 eV). For example, a laser at 1575 nm will leave 0.2 K of recoil energy, less than the ion sample's typical temperature or energy dispersion, to the neutral H. The fraction of resulting atoms with energy below 0.5 K can remain trapped in a 1 T trap depth superposed magnetic trap and could be detected using the sensitive technique [3]. These cold H can loaded into the ALPHA [4] antihydrogen trap at CERN toward direct spectroscopic comparison of both conjugated species beyond 13 significant figures. The production is scalable and adaptable to different species, including deuterium and tritium, which is relevant for neutrino mass and fusion research.

[1] - Azevedo, L.O.A., Costa, R.J.S., Wolff, W. et al. Adaptable platform for trapped cold electrons, hydrogen and lithium anions and cations. Commun Phys6, 112 (2023).
[2] - Sacramento, R. L. et al. Matrix Isolation Sublimation: an apparatus for producing cryogenic beams of atoms and molecules. Rev. Sci. Instrum.86, 073109 (2015).
[3] - Cesar, C. L. A sensitive detection method for high resolution spectroscopy of trapped antihydrogen, hydrogen and other trapped species. J. Phys. B49, 074001 (2016).
[4] - Ahmadi, M. et al. Characterization of the 1S-2S transition in antihydrogen. Nature557, 71 (2018).

Speaker: Levi Oliveira De Araujo Azevedo (Federal University of Rio de Janeiro (BR))

ECCTI_Levi.pptx

104 Gravity experiments with magnetically confined antihydrogen in ALPHAg.

The hydrogen atom has been studied extensively throughout history and provides the most precisely measured systems in physics. Antihydrogen has a significantly shorter history of study but the same potential for precision physics measurements. Comparisons between hydrogen and antihydrogen then offer the possibility to test fundamental symmetries such as charge, parity, and time reversal (CPT) symmetry at high precision.

The antihydrogen laser physics apparatus (ALPHA) at CERN produces and traps antihydrogen atoms in a magnetic minimum and studies its atomic spectrum. The latest venture for the ALPHA collaboration has been a new experiment, ALPHAg, aiming to observe the motion of antimatter in Earth’s gravitational field for the first time. As CPT makes no assertion about the motion of antimatter in Earth’s gravitational field this is a test of the equivalence principle.

Antihydrogen atoms are confined in a vertical magnetic minimum trap, the trapping potential is then different between the top and bottom of the trap by -mgΔh, where m is the antihydrogen mass, g is the gravitational acceleration and h is the height. When the vertical confining field is then removed during a slow magnetic release, antihydrogen escape in a direction favouring the gravitational acceleration. The difference in trapping potential is equivalent to a magnetic field difference of approximately $4× 10^{-4}$ T. It follows then that by intentionally adding a magnetic bias to the trap, one can find a bias that balances the effect of gravity. As the magnetic field is changed from 1.7 T to 1 T over 20 seconds during the release, it is necessary to control and measure the magnetic fields at each end of the magnetic trap to a higher precision than the gravitational potential difference.

I will discuss the systematic studies of these magnetic fields using electron plasmas in a Penning-Malmberg trap [1] and the magnetic release experiment results that enabled the first determination of the gravitational acceleration of antihydrogen, $a_\bar{g}$ = (0,75 ± 0,13 (stat. + syst.) ± 0,16 (simulation))g where g = 9.81 $\mathrm{m/s^2}$ [2].

[1] Electron cyclotron resonance (ECR) magnetometry with a plasma reservoir, E. D. Hunter ; A. Christensen ; J. Fajans ; T. Friesen ; E. Kur ; J. S. Wurtele Phys. Plasmas 27, 032106 (2020)

[2] Observation of the effect of gravity on the motion of antimatter, The ALPHA collaboration, Nature volume 621, pages716–722 (2023)

Speaker: Adam Powell (Dep. of Phys. and Astronomy University of Calgary (CA))

Powell_ECCTI_2024.pdf

Powell_ECCTI_2024.pptx

105 Hyperfine spectroscopy of antihydrogen with microwaves

For CPT symmetry to be conserved, the energy spectrum of both matter and antimatter atoms should be identical. The ALPHA collaboration uses antihydrogen, the antimatter counterpart of hydrogen, to perform CPT symmetry tests.

Microwave spectroscopy techniques were applied in the ALPHA experiment to observe, for the first time, the transition between hyperfine energy levels of antihydrogen. It is known as the positron spin resonant (PSR) transition and is induced by flipping the spin of the positron.
However, the transition produced by flipping the spin of the antiproton, known as nuclear magnetic resonant (NMR) transition, has only been measured in hydrogen, not on antihydrogen.

I will present the recent progress made to improve the PSR measurement and to enable a precise measurement of the NMR transition.

Speaker: Alberto Jesus Uribe Jimenez (Dep. of Phys. and Astronomy University of Calgary (CA))

HFS.pdf

HFS.pptx

106 Towards an ion trap source of cold atomic hydrogen

Understanding the origins of the cosmos has been a much sought after pursuit. One of the greatest mysteries is the composition of the universe itself, which deviates from the Standard Model predictions, since observations indicate that it is made almost entirely out of matter [1]. These observations paved the way for experiments that directly compare matter and antimatter, with the latest one being on the effect of gravity on antimatter [2].

A novel scheme for producing cold, magnetically trappable atomic hydrogen has been proposed [3]. The whole process relies on the production of Ba+/BaH+ ions through laser ablation of a solid BaH2 target, trapping these ions, laser cooling Ba+ and thus sympathetically cooling BaH+ ions, and finally photodissociating BaH+ ions to produce atomic hydrogen. We designed a new experimental setup, with a Paul trap as the main feature, as a proof of concept of the proposed scheme.
Here, I present our first results on the trapping and laser cooling of Ba+ ions extracted from a Ba target, as well as removing BaO, that was formed during handling the target, from its surface. Next phase of the experiment will use a BaH2 target and will result in the production of hydrogen. These techniques are compatible with the current generation antihydrogen experiments [4], since they all use ion traps to form antihydrogen, and make the whole scheme suitable for loading hydrogen into an antihydrogen experiment, for the direct comparison of the two species.

[1] G. Steigman. Observational tests of antimatter cosmologies. Annual review of astronomy and astrophysics 14 (1), 339 – 372 (1976).
[2] E. K. Anderson, C. J. Baker, W. Bertsche, et al. Observation of the effect of gravity on the motion of antimatter. Nature 621, 716–722 (2023).
[3] S. A. Jones. An ion trap source of cold atomic hydrogen via photodissociation of the BaH+ molecular ion. New J. Phys. 24, 023016 (2022).
[4] G. Andresen, M. Ashkezari, M. Baquero-Ruiz, et al. Trapped antihydrogen. Nature 468, 673–676 (2010).

Speaker: Nikolaos Efthymiadis (PhD student, University of Groningen, Netherlands)

EECTI 12.07.2024.pptx

Coffee break

eccti_coffeebreaks.pdf

eccti_coffeebreaks.pptx

Quantum Information & Computing

Convener: Edgar Brucke (ETH Zurich)

107 Demonstration of fault-tolerant Steane quantum error correction

Encoding information redundantly in quantum error correcting (QEC) codes is a way – perhaps the only way – to protect quantum information processors from the harmful effects of noise that impede large-scale computation. However, the execution of QEC itself is subject to faults which can transform and spread uncontrollably unless fault-tolerant design principles are applied as well. The consequence of this is that device capabilities, noise profile, QEC code, and correction scheme are all influencing each other.
In my talk I will present the first experimental demonstration of Steane QEC [1] which in combination with the transversal CNOT and full qubit connectivity minimizes the necessary coupling between data and auxiliary qubit register. We demonstrate the benefits of Steane error correction over previously demonstrated universal, fault-tolerant gate implementations [2] using traditional flag-based syndrome readout with three different types of codes of increasing code distances, establishing experimental Steane QEC as a competitive paradigm for fault-tolerant quantum computing.
[1] Postler, Lukas, et al. "Demonstration of fault-tolerant Steane quantum error correction." arXiv preprint arXiv:2312.09745 (2023).
[2] Postler, Lukas, et al. "Demonstration of fault-tolerant universal quantum gate operations." Nature 605.7911 (2022): 675-680.

Speaker: Dr Christian Marciniak (Universität Innsbruck)

Marciniak_ECCTI_Steane.pptx

108 Cycle Error Reconstruction on a trapped ion quantum computer

The presence of noise in quantum system makes the precise and efficient characterization of errors necessary. A myriad of benchmarking and tomography routines have been developed over the years to address this challenge. However, most of these suffer from scalability problems in implementation and the information extracted is frequently lacking in predictive or diagnostic utility. A major challenge towards practically useful error characterization techniques is to determine which errors of the exponentially many possible are relevant. The cyclic error reconstruction (CER) protocol tackles this issue by producing error marginals successively, giving the experimenter the choice of how much knowledge is extracted. CER is an extension of the cycle benchmarking protocol expanding its diagnostic utility – giving insight not only in how large the overall error is but also of its origin. In contrast to randomized benchmarking CER uses only single-qubit Pauli twirling and therefore is amenable to characterize multi-qubit processes. Here we apply the CER protocol to a trapped ion quantum computer learning error rates and crosstalk of gates in their natural context scaling from a single qubit gate to logical gadgets.

Speaker: Robert Freund

CER_ECCTI_Freund.pdf

CER_ECCTI_Freund.pptx

109 Focusing of microwave-driven gate interactions using dynamical decoupling

In trapped-ion quantum computing, quantum logic gates are often performed using lasers. Alternatively, gates can also be driven by microwave fields for which the technology is cheaper and more reliable, making it simpler to scale up. However, due to their centimetre wavelength, microwaves cannot be focused to a small spot size, making it difficult to address an individual ion within a cluster of ions confined by the same potential well.

We have proposed and demonstrated a method to enable microwave-driven entangling gate operations only in micron-sized zones, corresponding to $10^{-5}$ microwave wavelengths, whilst suppressing this interaction everywhere else [1]. This is done by utilising the variation in phase of a microwave-field across a surface trap. We find that the required interaction introduces $3.7(4) \times 10^{-4}$ error per emulated gate in a single-qubit benchmarking sequence. We then model the scheme for a 17-qubit ion crystal, and find that any pair of ions should be addressable with an average crosstalk error of $\sim 10^{-5}$.

[1] M. C. Smith et al., arXiv:2309.02125 (2023).

Speaker: Molly Smith (University of Oxford)

molly_talk (1).pptx

110 Towards High-Fidelity Microwave Gates on Microfabricated Ion-Traps

Trapped ions have proved to be the leading quantum computing platform, due to their long coherence times and simple reproducibility. The design of modular architectures is also facilitated, which is crucial for a scalable, universal quantum computer. Our blueprint for a trapped-ion based quantum computer outlines operating with global microwave (MW) fields to dress the ground-state hyperfine manifold of $^{171}Yb^+$ ions [1]. By applying individually controlled static (DC) voltages, ions can be effectively shuttled around and between modules [2], while modulated radio-frequency (RF) signals are utilised to implement quantum logic gate operations [3].

We have further developed microfabricated surface traps featuring X-junction arrays with embedded current-carrying wires (CCWs) able to provide a controllable magnetic field gradient [4]. The imminent way forward is the characterisation of these novel chips which serve as the modules of our scalable architecture. In addition, demonstration of high-fidelity single and two-qubit gate operations will be enabled by quantum control techniques designed for more robust entanglement gates [5].

[1] B. Lekitsch, S. Weidt, A. G. Fowler, K. Mølmer, S. J. Devitt, C. Wunderlich, and W. K.Hensinger, “Blueprint for a microwave trapped ion quantum computer”, Science Advances 3 (2017).

[2] M. Akhtar, F. Bonus, F. R. Lebrun-Gallagher et al., “A high-fidelity quantum matter-link between ion-trap microchip modules”, Nature Communications 14, 531 (2023).

[3] S. Weidt, J. Randall, S. C. Webster et al., “Trapped-ion quantum logic with global radiation fields”, Physical Review Letters 117 (2016).

[4] Z. D. Romaszko, S. Hong, M. Siegele et al. “Engineering of microfabricated ion traps and integration of advanced on-chip features”, Nat Rev Phys 2, 285–299 (2020).

[5] C. H. Valahu, I. Apostolatos, S. Weidt and W. K. Hensinger, “Quantum control methods for robust entanglement of trapped ions”, J. Phys. B: At. Mol. Opt. Phys. 55 204003 (2022).

Speaker: Petros Zantis (University of Sussex - Ion Quantum Technology group)

PetrosZantis-ECCTI2024.pdf

Lunch break

Lab tours

Social Activity (optional): Cable car ride to Hafelekar for a stunning view of the Alps