We create polarization entangled, spectrally broadband photon pairs from parametric down-conversion in semiconductor Bragg-reflection waveguides. We show, how to adjust the coherence of the polarization entangled states by controlling the relative temporal delay between a pair of photons with a birefringent retarder.
Otherwise, the slight temporal walk-off of the photon pair, which is caused...
Different variants of Bell inequalities, such as CHSH and CH, are known to
be equivalent when evaluated on nonsignaling outcome probability distributions. However,in experiments, these probability distributions are estimated using a finite number of samples. Therefore the nonsignaling conditions are only approximately satisfied: the robustness of the violation depends on the chosen inequality...
Quantum memories matched to single photon sources will form an important cornerstone of future quantum-network technology. We demonstrate such a memory in warm Rb vapor with on-demand storage and retrieval, based on electromagnetically induced transparency. We test the memory with laser pulses, attenuated to the single photon level. Their bandwidth is chosen to be 660(10) MHz to simulate the...
Quantum theory predicts that entanglement can also persist in macroscopic physical systems, albeit difficulties to demonstrate it experimentally remain. Recently, significant progress has been achieved and genuine entanglement between up to 2900 atoms was reported. Here we demonstrate 16 million genuinely entangled atoms in a solid-state quantum memory prepared by the heralded absorption of a...
A basic task necessary for quantum information processing is the ability to faithfully transfer quantum states between distant quantum systems. A very promising platform for the implementation of quantum computers with outstanding controllability consists of superconducting quantum circuits, interacting via photon exchange in the microwave regime, which however are extremely sensitive to...
Super-resolution-microscopy is a fast evolving field, revolutionizing traditional optical microscopy. These techniques enhance the precision of optical microscopy beyond the standard resolution limit and reach resolutions of a few nanometers. Here we show that, depending on the polarization of the light emitted by the observed particle, systematic wavelength-scale errors can occur when...
The projective simulation (PS) model is a physical approach to artificial intelligence. In the PS model, learning is realized by internal modification of the episodic memory network, both in terms of its structure and the weights of its edges. Through interactions with a task environment, the PS memory network adjusts itself dynamically, so as to increase the probability of performing better...
Coherent scattering of light from ultracold atoms involves exchange of energy and momentum so that particles can spontaneously form periodic configurations that simultaneously maximize light scattering and minimize the atomic potential energy. Similar to self-ordering with Bose-Einstein condensates (BECs) inside an optical resonator we study periodic pattern formation in free space by...
In this presentation, I will talk about spatial spin and density self-ordering of a transversely-pumped two-component Bose-Einstein condensate coupled into a single mode of a linear cavity. The onset of the Dicke superradiance phase transition is marked by a simultaneous appearance of a crystalline density order and a spin-wavev order. The self-ordering in our system is driven by a...
Spontaneous emission of atoms in free space is modified by other atoms in close vicinity inducing collective super- and sub-radiance. For two atoms with a single decay channel the antisymmetric superposition state of the two single excited states will not decay spontaneously. No such excited two-atom dark state exists, if the excited state has two distinguishable independent decay channels....
Matter-wave interferometry imprints a periodic structure onto a molecular beam. This provides a ruler on the nanometer scale for measuring a variety of electronic properties of biomolecules in the same setup. Here we demonstrate interference-assisted metrology with provitamin A, vitamin E and vitamin K1 for the first time. The shift of the interference fringes in a static electric field...
On our atomchip setup a one-dimensional Bose gas of 87Rb is cooled down to the transverse groundstate of the trapping potential. The wave function of the condensate is manipulated by displacing the potential following a trajectory defined by optimal control. Thus superpositions of transverse vibrational states are prepared.
Their dynamics is probed by measuring the transverse momentum...
We study a system of interacting fermions with large spin and SP(N) symmetry. From the Fermi liquid theory we find that the effective mass and inverse compressibility are always enhanced in the presence of interactions. Concerning magnetism, the Wilson ratio can be enhanced, indicating that the system can be made closer to a magnetic instability, in contrast to the SU(N) scenario. We conclude...
We present our spectroscopic and metrological investigations related to the development of next generation high performance vapor-cell atomic clocks. Such precision instruments are crucial for applications such global satellite navigation systems and network synchronisation. Our studies concern both basic atoms-photons resonant interactions (in the microwave and optical domains) and more...
Positronium is an excellent system to test bound state QED theory to high precision, since it is almost exlusively governed by the electromagnetic force and does not exhibit finite size effects which plague measurements of protonic atoms.
Numerous precise experiments have therefore been conducted in the past to measure the hyperfine splitting of Positronium. However, these experiments show...
We are investigating the use of laser-cooled anionic molecules to sympathetically cool antiprotons confined in the same trapping potential, which is of interest for antimatter experiments at CERN. A test setup to produce cold ground state C2- molecules is currently being commissioned.
This setup will be presented, together with a theoretical study on the feasibility of several laser cooling...
We report on measurements and simulations on a superconductor tube in the presence of inhomogeneous magnetic fields in a cryogenic environment. The effect is studied using Hall sensors in a table top experiment. The suppression of external magnetic fields in a controlled manner is important for precision experiments in cryogenic environments in atomic physics and antimatter experiments. Also...
The Pauli Exclusion Principle (PEP) is the foundation for our understanding of physics where systems of fermions are concerned. Therefore, it is important to make precision tests of the PEP. In a pioneering experiment, Ramberg and Snow supplied an electric current to a Cu target, and searched for PEP violating atomic transitions of the “fresh" electrons from the current. The non-existence of...
