Feedback in a cavity QED system for control of quantum beats
1 Joint Quantum Institute, University of Maryland and NIST, College Park, MD 20742, USA
2 IIMAS, Universidad Nacional Autonoma de México, México 04510, DF, México
3 Department of Physics, University of Auckland, Private Bag 92019, Auckland, New Zealand
a e-mail: firstname.lastname@example.org
Conditional measurements on the undriven mode of a two-mode cavity QED system prepare a coherent superposition of ground states which generate quantum beats. The continuous system drive induces decoherence through the phase interruptions from Rayleigh scattering, which manifests as a decrease of the beat amplitude and an increase of the frequency of oscillation. We report recent experiments that implement a simple feedback mechanism to protect the quantum beat. We continuously drive the system until a photon is detected, heralding the presence of a coherent superposition. We then turn off the drive and let the superposition evolve in the dark, protecting it against decoherence. At a later time we reinstate the drive to measure the amplitude, phase, and frequency of the beats. The amplitude can increase by more than fifty percent, while the frequency is unchanged by the feedback.
© Owned by the authors, published by EDP Sciences, 2013
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