Recovering coherence with use of quantum feedback

Shikun Zhang, Guofeng Zhang

Thomas Vanderbruggen, Ralf Kohlhaas, Andréa D Bertoldi +4 more

Weak measurements provide new ways to observe and control quantum systems. Here we use weak non-destructive measurements in a feedback scheme to protect an atomic ensemble in a coherent superposition against a simple decoherence model. The feedback efficiency, defined as the ability to recover the coherence of the initial state, is studied versus the number of photons in the probe beam. This allows us to precisely characterize the trade-off between information retrieval and destructivity. The lifetime of the coherent spin state is increased by one order of magnitude when the correction cycle is iterated.

Felix Cheung

Gavin Crowder, H. J. Carmichael, Stephen Hughes

We describe an efficient approach to modeling cavity quantum electrodynamics (QED) with a time-delayed coherent feedback using quantum trajectory simulations. An analytical set of equations is derived to exploit the advantages of trajectories in the presence of the non-Markovian dynamics, where adjustments to the standard stochastic dynamics are discussed. In the weak excitation regime, we first verify that our approach recovers known results obtained with other simulation methods and demonstrate how a coherent feedback loop can increase the photon lifetime in typical cavity-QED systems. We also highlight the underlying stochastic dynamics. We then explore the nonlinear few-photon regime of cavity QED, under the restriction of at most one photon at a time in the feedback loop. In particular, we show how feedback affects the cavity photoluminescence (populations versus laser detuning) and describe how one must account for conditioning in the presence of feedback; specifically, the system observables must be conditioned on no photon detections at the feedback output channel occurring.

José Tito Mendonça, Hugo Terças

Jing Zhang, Yu-xi Liu, Re-Bing Wu +2 more