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

Journal Article · Tue Nov 15 04:00:00 EST 2005 · Physical Review. A

DOI:https://doi.org/10.1103/PHYSREVA.72.0· OSTI ID:20786588

Felinto, D; Chou, C W; Riedmatten, H de; Polyakov, S V; Kimble, H J ^[1]

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1. Norman Bridge Laboratory of Physics 12-33, California Institute of Technology, Pasadena, California 91125 (United States)

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 et al. 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.

• OSTI ID: 20786588
• Journal Information: Physical Review. A, Journal Name: Physical Review. A Journal Issue: 5 Vol. 72; ISSN 1050-2947; ISSN PLRAAN
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
COMPARATIVE EVALUATIONS
CONTROL
CORRELATIONS
DATA TRANSMISSION
DISTANCE
ENERGY SPECTRA
EXCITATION
GROUND STATES
HYPERFINE STRUCTURE
INFORMATION THEORY
MAGNETIC FIELDS
OPTICAL PUMPING
PHOTONS
POLARIZATION
PULSES
RAMAN EFFECT
RAMAN SPECTROSCOPY
SWITCHES
TRAPS
ZEEMAN EFFECT