Quantum computers are making significant progress in their performance as measured by their scale, speed, and quality. For instance, in 2022 IBM Quantum announced a 433-qubit quantum processor and a factor of 10 increase in circuit execution speed. Furthermore, coherence times and gate fidelities have also improved as exemplified by T1 times on devices with 127 qubits which typically range...
Non-classicality is a key resource for quantum technologies and requires its proper and efficient quantification. Manifestation of non-classicality in the form of various phenomena such as existence of non-commutative observables and fundamental invasiveness of measurements suggest different ways to its identification. An efficient recipe is offered by processes featuring indefinite causal...
Kernel methods in Quantum Machine Learning (QML) have attracted significant attention as a potential candidate for quantum advantage in data analysis. In this work, we study the trainability of quantum kernels from the perspective of the resources needed to accurately estimate kernel values. We identify four sources that can lead to exponential concentration and provide associated...
Transmon qubits based on superconducting circuits are the most popular platform in NISQ era and have witnessed many significant advancements. However, there are several challenges, such as flux noise, crosstalk between qubits, and thermal load due to flux bias. A possible solution are semiconductor-superconductor hybrid systems. The weak link in transmon is substituted by a gate-tunable...
Parameterized quantum circuits serve as ansätze for solving variational problems and provide a flexible paradigm for programming near-term quantum computers. Here we discuss three fundamental criteria for this paradigm to be effective: expressibility, trainability and generalisability. We will introduce these concepts and present recent analytic progress quantifying to what extent these...
Hole spin qubits are promising for large-scale quantum computers because of their large spin-orbit interaction (SOI).
I will present schemes to engineer SOI, optimizing quantum information processing. Large SOI mediates strong and tunable coupling between spins and photons, that can be engineered to be longitudinal. This coupling enables exact protocols for fast high-fidelity two-qubit...
Recent spin-qubit experiments demonstrate gate operations and readout well within 1% error rate. This is the error threshold of the surface code assuming that gate errors, measurement errors, and data qubit errors occur with the same probability. Recent developments in error correction codes present opportunities to improve the threshold and reduce connectivity requirements compared to...
Quantum computation has captivated the minds of many for almost two decades. For much of that time, it was seen mostly as an extremely interesting scientific problem. In the last few years, we have entered a new phase as the belief has grown that a large-scale quantum computer can actually be built. Quantum bits encoded in the spin state of individual electrons in silicon quantum dot arrays,...
Quantum process learning is emerging as an important tool to study quantum systems, but little attention has been paid to whether dynamics of quantum systems can be learned without the system and target directly interacting. Here we provide bounds on the sample complexity of learning unitary processes incoherently and show that, if arbitrary measurements are allowed, then any efficiently...
The realization of highly stable, controllable, and accessible hole spin qubits is strongly dependent on the quality of the materials hosting them. Ultra-clean germanium/silicon-germanium heterostructures in quantum wells (QWs) are the perfect candidates. Due to their large scalability potential, they pave the way towards the development of realistic and reliable solid state, all-electric...
High-quality semiconductor heterostructures build the basic ingredient facilitating quantum transport experiments including the promising field of semiconductor spin qubits. Ge quantum wells have recently emerged as a suitable platform for fast spin qubits, due to a combination of favorable properties of the confined states. The Ge platform is furthermore interesting as the Fermi level pinning...
I have a small research group in Innsbruck that focuses on developing methods to entangle quantum systems in remote locations. Our quantum systems of choice are strings of trapped atomic ions. The strings are confined in linear Paul traps with an integrated optical cavity for the collection of 854 nm photons. In this talk I’ll briefly introduce our main experimental methods and then give an...
In the past few years Germanium has attracted lot of attention as a platform for spin qubits, due to the low effective mass, strong spin orbit interaction, which allows electrically driven spin qubits, and its potential for co-integration with superconducting technology.
From 2018 and within just three years a Loss-DiVincenzo (LD), a singlet-triplet hole spin qubit, two-qubit gate devices and...
By leveraging industrial CMOS manufacturing processes, spin qubits in silicon are a promising approach to achieving scalable quantum computing. While electron spin qubits have reached many milestones, hole spins in silicon present an exciting new platform, allowing for fast, all-electrical qubit control, absence of valleys and low susceptibility to hyperfine noise. Here, we present recent...
Dispersive gate sensing, where a resonator is directly attached to a quantum dot gate, is a promising spin qubit readout technique. We discuss a potential limitation of this approach arising from capacitive crosstalk. We find that an ac voltage modulation on a plunger gate of a finFET double quantum dot can induce a 20 times larger signal on the neighboring barrier gate attached to a tank...
Long-range couplers based on individual microwave photons are desirable for realizing spin-based quantumcomputing.
Here, we present a spin-photon interface based on intrinsic spin-orbit interaction in a zinc-blende InAs nanowire. The nanowire hosts a double-quantum dot with epitaxial crystal-phase tunnel barriers and strong spin-orbit interaction. These properties immensely simplify device...
Silicon with its long coherence time of spins of localized electrons is a candidate for quantum information processing . Among quantum materials compatible with Si there is germanium (Ge), which has however a 4.2% mismatch. Such a mismatch introduces strains in Si/Ge heterostructures hindering mobility. Thus, scattering must be minimized by diminishing strains. Interestingly, electron and hole...
We have built a parametric amplifier with a Josephson field effect transistor (JoFET) as the active element inside a half-wave transmission line resonator. The JoFET has been made from an aluminum-indium arsenide superconductor-semiconductor heterostructure with a controlling top gate. The device’s resonant frequency is field-effect tunable over a range of 2 GHz. The JoFET amplifier has 20 dB...
