QUROPE Quantum Information Processing and Communication in Europe

Quantum noise correlations have been employed in several areas of physics, including condensed matter, quantum optics and ultracold atoms, to reveal the non-classical states of the systems. To date, such analyses have mostly focused on systems in equilibrium. In this paper, we show that quantum noise is also a useful tool for characterizing and studying the non-equilibrium dynamics of a one-dimensional (1D) system.

We theoretically analyze a Mach-Zehnder interferometer with trapped condensates and find that it is surprisingly stable against the nonlinearity induced by interparticle interactions. The phase sensitivity, which we study for number-squeezed input states, can overcome the shot noise limit and be increased up to the Heisenberg limit provided that a Bayesian or maximum-likelihood phase estimation strategy is used. We finally demonstrate the robustness of the Mach-Zehnder interferometer in the presence of interactions against condensate oscillations and a realistic atom-counting error.

Cavity quantum electrodynamics describes the fundamental interactions between light and matter, and how they can be controlled by shaping the local environment. For example, optical microcavities allow high-efficiency detection and manipulation of single atoms. In this regime, fluctuations of atom number are on the order of the mean number, which can lead to signal fluctuations in excess of the noise on the incident probe field.

The ability to sensitively detect individual charges under ambient conditions would benefit a wide range of applications across disciplines. However, most current techniques are limited to low-temperature methods such as single-electron transistors, single-electron electrostatic force microscopy and scanning tunnelling microscopy. Here we introduce a quantum-metrology technique demonstrating precision three-dimensional electric-field measurement using a single nitrogen-vacancy defect centre spin in diamond. An a.c.

We report strong coupling between an ensemble of nitrogen-vacancy center electron spins in diamond and a superconducting microwave coplanar waveguide resonator. The characteristic scaling of the collective coupling strength with the square root of the number of emitters is observed directly. Additionally, we measure hyperfine coupling to 13C nuclear spins, which is a first step towards a nuclear ensemble quantum memory.

D. Meschede (P6 UBONN), invited talk, Splitting, walking and blinding a single neutral atom

D. Meschede (P6 UBONN), invited talk, Coherent Splitting, Rocking and Blinding of Single Atoms

D. Meschede (P6 UBONN), invited talk, Einzelne Atome kohärent steppen, schaukeln und blenden

A. Alberti (P6 UBONN), poster, Discrete interferometer with individual trapped atoms

M. Martinez-Dorantes (P6 UBONN), poster, Control of Refractive Index and Motion of a Single Atom by Quantum Interference

A. Alberti (P6 UBONN), poster, Discrete interferometer with individual trapped atoms

P.G. Petrov (P5 IMPERIAL), poster, An array of integrated atom-photon junctions