QUROPE Quantum Information Processing and Communication in Europe

We explore the challenges posed by the violation of Bell-like inequalities by d-dimensional systems exposed to imperfect state-preparation and measurement settings. We address, in particular, the limit of high-dimensional systems, naturally arising when exploring the quantum-to-classical transition. We show that, although suitable Bell inequalities can be violated, in principle, for any dimension of given subsystems, it is in practice increasingly challenging to detect such violations, even if the system is prepared in a maximally entangled state.

Entangled atomic states, such as spin-squeezed states, represent a promising resource for a new generation of quantum sensors and atomic clocks. We demonstrate that optimal control techniques can be used to substantially enhance the degree of spin squeezing in strongly interacting many-body systems, even in the presence of noise and imperfections. Specifically, we present a protocol that is robust to noise and outperforms conventional methods. Potential experimental implementations are discussed.

Atom chips provide compact and robust platforms towards the implementation of practical quantum technologies. A quick and faithful preparation of arbitrary input states for these devices is crucial but represents a challenging experimental task. This is especially difficult when the dynamical evolution is noisy and unavoidable setup imperfections have to be considered. Here, we experimentally prepare with very high fidelity nontrivial superpositions of internal states of a rubidium Bose-Einstein condensate realized on an atom chip.

We study the equilibrium properties of the one-dimensional disordered Bose–Hubbard model by means of a gauge-adaptive tree tensor network variational method suitable for systems with periodic boundary conditions. We compute the superfluid stiffness and superfluid correlations close to the superfluid to glass transition line, obtaining accurate locations of the critical points.

Abstract:

FRONTIERS IN ULTRACOLD FERMI GASES
90 years after the "birth" of fermions in Florence
Florence (Italy), 21-23 March 2016

Dear atom opticians, we would like to announce the 22nd Young Atom Opticians conference (YAO) to be held in Munich - on the Garching research campus - from Sunday, 21st to Friday, 26th of February 2016. The YAO conference is an international meeting aiming at PhD and Master students working in fields related to Quantum Optics and Atomic and Molecular Physics. It gained reputation as an excellent platform for young researchers to present their work and to establish networks among postgraduate researchers in the European atomic physics community.

A participatory workshop on Quantum Technologies and Industry was held in Brussels on 6 May 2015. The aim was to identify what could be the markets for quantum technologies, and how these could be industrialised. The workshop report (available here) summarises the discussions and the action plan which emerged as a conclusion.

The paper, authored by Norbert Kalb, Andreas Reiserer, Stephan Ritter, and Gerhard Rempe has been published on 2 June 2015 as Phys. Rev. Lett. 114, 220501 (2015).

Combining techniques of cavity quantum electrodynamics, quantum measurement, and quantum feedback, we have realized the heralded transfer of a polarization qubit from a photon onto a single atom with 39% efficiency and 86% fidelity. The reverse process, namely, qubit transfer from the atom onto a given photon, is demonstrated with 88% fidelity and an estimated efficiency of up to 69%. In contrast to previous work based on two-photon interference, our scheme is robust against photon arrival-time jitter and achieves much higher efficiencies.