QUROPE Quantum Information Processing and Communication in Europe

We propose to implement the Jaynes-Cummings model by coupling a few-micrometer large atomic ensemble to a quantized cavity mode and classical laser fields. A two-photon transition resonantly couples the single-atom ground state |g> to a Rydberg state |e> via a non-resonant intermediate state |i>, but due to the interaction between Rydberg atoms only a single atom can be resonantly excited in the ensemble.

The number of defects which are generated upon crossing a quantum phase transition can be minimized by choosing properly designed time-dependent pulses. In this work we determine what are the ultimate limits of this optimization. We discuss under which conditions the production of defects across the phase transition is vanishing small.

NMR spectroscopy

Quantum Control

Optimal Control

Dipolar Couplings

Partially Oriented Spectroscopy

We demonstrate feedback cooling of the motion of a single rubidium atom trapped in a high-finesse optical resonator to a temperature of about 160 \mu K. Time-dependent transmission and intensity-correlation measurements prove the reduction of the atomic position uncertainty. The feedback increases the 1/e storage time into the one second regime, 30 times longer than without feedback. Feedback cooling therefore rivals state-of-the-art laser cooling, but with the advantages that it requires less optical access and exhibits less optical pumping.

Researchers claim to have fabricated the first all-optical transistor on a silicon chip. This device allows the transmission of light emitted by one laser to be governed by the intensity of another.

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Please mark your calendars for the European Workshop "From Quantum Foundations to Quantum Technologies - Challenges for Europe", which will take place on 15 December 2010 in Vienna, Austria. The workshop will host international key players in the field to jointly explore the prospects for future European quantum research at the interface between foundations and applications. A detailed program will soon be available at

http://www.quantum.at/talksevents/eu-workshop-from-quantum-foundations-t...

• Mesoscopic Josephson junctions
• Charge and phase qubits
• Current fluctuations and cross correlations
• Graphene and hybrid systems
• Sensor/amplifier applications

Solid-state quantum optics, nanophotonics, quantum dots, photonic crystals, plasmonics, multiple scattering and Anderson localization of quantum light

An optical microcavity with small mode radius is used to measure the local density of a cold atom cloud. Atom densities below 1 per cavity mode volume are measured with signals near the photon shot-noise limit. Atom detection is fast and efficient, reaching fidelities in excess of 97% after 10 us and 99.9% after 30 us. Notably, the fluctuations of the detected photon counts are smaller than expected for Poissonian distributions of atoms probed with Poissonian light fields.

We investigate the use of a Bose-Einstein condensate trapped on an atom chip for making interferometric measurements of small forces. A fundamental limit on sensitivity is imposed by the noise in the energy difference of the split condensates, which we measure and explain. We also consider systematic errors. A leading effect is the variation of rf magnetic field in the trap with distance from the wires on the chip surface. This can produce energy differences that are comparable with those due to gravity.