QUROPE Quantum Information Processing and Communication in Europe

M. Brune (P2a CNRS), invited talk, Manipulating and probing microwave fields in a cavity by quantum nodemolition photon counting: State stabilization by quantum feed-back.

G. Morigi (P8 Universität des Saarlandes), invited talk, Ultracold atoms in optical resonators.

P. Treutlein (P11 LMU München), invited talk, Atom-chip based generation of entanglement for quantum metrology.

T. Schumm (P12 TU Wien), talk, Probing one-dimensional Bose gases on the single particle level.

K. Hammerer(P4b OEAW), talk, Interfacing Opto-Mechanics with Atoms.

Physicists at MPQ control the optical properties of a single atom!

Due to the continued miniaturization of computer chip components, we are about to cross a fundamental boundary where technology can no longer rely on the laws of the macroscopic world. With this in mind, scientists all over the world are researching technologies based on quantum effects that can be used to communicate and process information. One of the most promising developments in this direction are quantum networks in which single photons communicate the information between different nodes, e.g. single atoms. There the information can be stored and processed. A key element in these systems is Electromagnetically Induced Transparency (EIT), an effect that allows to radically change the optical properties of an atomic medium by means of light. Previously, scientists have studied this effect and its amazing properties, using atomic ensembles with hundreds of thousands of atoms. Now, scientists in the group of Prof. Gerhard Rempe, Director at the Max Planck Institute of Quantum Optics (MPQ) in Garching and Head of the Quantum Dynamics Division, have managed to control the optical response of a single atom using laser light (Nature, Advanced Online Publication, DOI: 10.1038 /nature09093). While representing a corner stone in the development of new quantum based technologies, these results are also fundamental for the understanding of how the quantum behaviour of single atoms can be controlled with light.

This will be a session open to all members of the QIP research community. The Program includes both European and non-European speakers and representatives of the European Commission.

We have fabricated and tested an atom chip that operates as a matter wave interferometer. In this communication we describe the fabrication of the chip by ion-beam milling of gold evaporated onto a silicon substrate. We present data on the quality of the wires, on the current density that can be reached in the wires and on the smoothness of the magnetic traps that are formed. We demonstrate the operation of the interferometer, showing that we can coherently split and recombine a Bose–Einstein condensate with good phase stability.

Perfect states are those quantum states from which a perfectly secure cryptographic key can be extracted. They present the basic unit of quantum privacy. In this work we show that all states belonging to this class violate a Bell inequality. This result establishes a connection between perfect privacy and non-locality in the quantum domain.

We investigate a setup where a cloud of atoms is trapped in an optical lattice potential of a standing-wave laser field which is created by retroreflection on a micromembrane. The membrane vibrations itself realize a quantum mechanical degree of freedom. We show that the center-of-mass mode of atoms can be coupled to the vibrational mode of the membrane in free space. Via laser cooling of atoms a significant sympathetic cooling effect on the membrane vibrations can be achieved. Switching off laser cooling brings the system close to a regime of strong coherent coupling.

We present a versatile and compact electron beam driven source for alkali metal atoms which can operate even with a heat dissipation of less than 1mW, and can therefore be implemented inside a closed cycle cryostat. Atoms are loaded into a Magneto-Optical Trap (MOT) and at a given thermal input power, loading rates three orders of magnitude higher than in a typical MOT loaded by an alkali metal dispenser are achieved.

A rigorous quantum theory of atomic collisions in the presence of radio frequency (rf) magnetic fields is developed and applied to elucidate the effects of combined dc and rf magnetic fields on ultracold collisions of Rb atoms. We show that rf fields can be used to induce Feshbach resonances, which can be tuned by varying the amplitude and frequency of the rf field.