15.20.Ca Cavity QED

Non-classical field state stabilization in a cavity by reservoir engineering


A. Sarlette, J.M. Raimond and P. Rouchon

We propose an engineered reservoir inducing the relaxation of a cavity field towards non-classical states. It is made up of two-level atoms crossing the cavity one at a time. Each atom-cavity interaction is first dispersive, then resonant, then dispersive again. The reservoir pointer states are those produced by a fictitious Kerr Hamiltonian acting on a coherent field. We thereby stabilize squeezed states and quantum superpositions of multiple coherent components in a cavity having a finite damping time.

Phase space tweezers for tailoring cavity fields by quantum Zeno dynamics


J.M. Raimond, C. Sayrin, S. Gleyzes, I. Dotsenko, M. Brune, S. Haroche, P. Facchi, S. Pascazio
Phys. Rev. Lett. 105, 213601 (2010)

Cavity Quantum Electrodynamics with a Rydberg blocked atomic ensemble


C. Guerlin, E. Brion, T. Essslinger, K. Mølmer
Phys. Rev. A 82, 053832 (2010)

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.

Cavity-enhanced atom detection with cooperative noise


J. Goldwin, M. Trupke, J. Kenner, A. Ratnapala, E. A. Hinds

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.

Cavity QED with an ultracold ensemble on a chip: prospects of strong magnetic coupling at finite temperatures


K. Henschel, H. Ritsch, J. Majer, J. Schmiedmayer
Phys. Rev. A, 82, 033810 (2010)

We study the nonlinear dynamics of an ensemble of cold trapped atoms with a hyperfine transition magnetically coupled to a resonant microwave cavity mode. Despite the minute single atom coupling one obtains strong coupling between collective hyperfine qubits and microwave photons enabling coherent transfer of an excitation between the long lived atomic qubit state and the mode. Evidence of strong coupling can be obtained from the cavity transmission spectrum even at finite thermal photon number.

Optical control of the refractive index of a single atom


Tobias Kampschulte, Wolfgang Alt, Stefan Brakhane, Martin Eckstein, René Reimann, Artur Widera, Dieter Meschede
Phys. Rev. Lett. 105, 153603 (2010)

The optical properties of an atomic medium can be changed dramatically by the coherent interaction with a near-resonant control light field: An optically dense medium can be rendered transparent and group velocities can be strongly reduced. So far the demonstration of this electromagnetically induced transparency (EIT) has relied on macroscopic ensembles of atoms probed by relatively intense light fields. Here we demonstrate the most elementary case, where the medium is formed by a single atom inside an optical cavity, probed by single photons.

Lossless state detection of single neutral atoms


Joerg Bochmann, Martin Mücke, Christoph Guhl, Stephan Ritter, Gerhard Rempe, David L. Moehring


Phys. Rev. Lett. 104, 203601 (2010)

We introduce lossless state detection of trapped neutral atoms based on cavity-enhanced fluorescence. In an experiment with a single 87-Rb atom, a hyperfine-state detection fidelity of 99.4% is achieved in 85 microseconds. The quantum bit is interrogated many hundred times without loss of the atom while a result is obtained in every read-out attempt. The fidelity proves robust against atomic frequency shifts induced by the trapping potential.

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