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arXiv:1908.07022 · Physica Scripta

Cavity-assisted squeezing and entanglement: non-adiabatic effects and optimal cavity-atomic ensemble matching

Natalia Masalaeva, Anton N. Vetlugin, I. V. Sokolov

Published Oct 30, 2019• 3 citations
arXivHTMLPDF

Abstract

Abstract We investigate theoretically quantum entanglement of light with the collective spin polarization of a cold atomic ensemble in cavity-assisted Raman schemes. Previous works concentrated mostly on the bad cavity limit where the signals are much longer than the cavity field lifetime. In view of atomic relaxation and other imperfections, there may arise a need to speed-up the light-atoms interface operation. By increasing the cavity field lifetime, one can achieve better light–matter coupling and entanglement. In our work, we consider the non-adiabatic effects that become important beyond the bad cavity limit in both low-photon and continuous variables regime. We find classical control field time profiles that allow one to retrieve from the cavity an output quantized signal of a predefined time shape and duration, which is optimal for the homodyne detection, optical mixing or further manipulation. This is done for a wide range of the signal duration as compared to the cavity field lifetime. We discuss an optimal cavity–atomic ensemble matching in terms of the cavity field lifetime which allows one to apply less intense control field and to minimize a variety of nonlinear effects, such as AC light shifts, four-wave mixing, etc, which may be potentially harmful to an experiment.

DOI
10.1088/1402-4896/ab52a2

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Abstract A promising platform for quantum information research relies on cavity coupled atomic spin-waves, enabling efficient operations such as quantum memories, quantum light generation and entanglement distribution. In this work, we study the strong coupling between non-classical collective spin excitations generated by Raman scattering in a cold 87 R b atomic ensemble, and a single cavity mode. We report on an intracavity spin wave to single photon conversion efficiency of up to χ = 0.75 ± 0.02 in the quantum domain, as evidenced by a violation of the Cauchy–Schwarz inequality. Our work establishes a relationship between the retrieval of an atomic spin wave in the non-classical regime and the vacuum Rabi splitting. We show that this relationship emerges within the efficiency spectrum, and we finally provide the optimal operational conditions to achieve the maximum intrinsic retrieval efficiency. Our data is well reproduced by simulations based on optical Bloch equations. This work deepens the understanding of cavity-enhanced spin wave readout and its potential applications.