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Control of decoherence in the generation of photon pairs from atomic ensembles

Felinto, D. and Chou, C. W. and de Riedmatten, H. and Polyakov, S. V. and Kimble, H. J. (2005) Control of decoherence in the generation of photon pairs from atomic ensembles. Physical Review A, 72 (5). Art. No. 053809. ISSN 1050-2947. http://resolver.caltech.edu/CaltechAUTHORS:FELpra05

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Abstract

We report an investigation to establish the physical mechanisms responsible for decoherence in the generation of photon pairs from atomic ensembles, via the protocol of Duan for long-distance quantum communication [Nature (London) 414, 413 (2001)] and present the experimental techniques necessary to properly control the process. We develop a theory to model in detail the decoherence process in experiments with magneto-optical traps. The inhomogeneous broadening of the ground state by the trap magnetic field is identified as the principal mechanism for decoherence. The theory includes the Zeeman structure of the atomic hyperfine levels used in the experiment, and the polarization of both excitation fields and detected photons. In conjunction with our theoretical analysis, we report a series of measurements to characterize and control the coherence time in our experimental setup. We use copropagating stimulated Raman spectroscopy to access directly the ground-state energy distribution of the ensemble. These spectroscopic measurements allow us to switch off the trap magnetic field in a controlled way, optimizing the repetition rate for single-photon measurements. With the magnetic field off, we then measure nonclassical correlations for pairs of photons generated by the ensemble as a function of the storage time of the single collective atomic excitation. We report coherence times longer than 10 mu s, corresponding to an increase of two orders of magnitude compared to previous results in cold ensembles. The coherence time is now two orders of magnitude longer than the duration of the excitation pulses. The comparison between these experimental results and the theory shows good agreement. Finally, we employ our theory to devise ways to improve the experiment by optical pumping to specific initial states.


Item Type:Article
Additional Information:©2005 The American Physical Society. Received 11 July 2005; published 9 November 2005. This work is supported by ARDA, by the Caltech MURI Center for Quantum Networks, and by the NSF. D.F. acknowledges financial support by CNPq (Brazilian agency). H.d.R. aknowledges financial support by the Swiss National Science Foundation.
Subject Keywords:quantum optics; quantum communication; Zeeman effect; hyperfine structure; stimulated Raman scattering; optical communication; ground states; information theory
Record Number:CaltechAUTHORS:FELpra05
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:FELpra05
Alternative URL:http://dx.doi.org/10.1103/PhysRevA.72.053809
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:3646
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:22 Jun 2006
Last Modified:26 Dec 2012 08:55

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