Optical properties of a quantum-noise-limited phase-sensitive amplifier
Lett, Paul D.
Rolston, Steven L.
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This dissertation is a summary of investigations on the optical properties of a quantum-noise-limited phase-sensitive amplifier (PSA). The PSA is implemented using four-wave mixing in hot Rb 85 vapor based on a double-Lambda atomic scheme. We experimentally demonstrate the ability of a PSA to pre-amplify quantum correlations in twin light beams produced by a phase-insensitive amplifier (PIA) before degradation due to loss and detector inefficiency. By including a PSA before loss, one is able to preserve the correlations as well as the two-mode squeezing level. We compare the results to simulations employing a simple quantum-mechanical model and find a good agreement. We have demonstrated that the cross-correlation between the two modes of a bipartite entangled state can be advanced by propagation through a PIA acting as a fast-light medium. The extra noise added by the PIA has been speculated to be the mechanism that limits the advance of entanglement, preventing the mutual information from traveling superluminally. As an extension of this phase-insensitive, gain-assisted, anomalous dispersion investigation, we explore the advance and delay of information transmitted through the PSA. We start with a two-mode squeezed state created by the PIA and measure the mutual information shared by the correlated quadratures. We then pass one of these two modes through a PSA and investigate the shift of the mutual information as a function of the PSA phase. In the case of a PSA, it is well known that no extra noise will be added to the quadrature with the correct input phase (e.g., the quadrature with the maximal amplification or the maximal deamplification). We find that there is no dispersion-like behavior at these two phases, however, the peak of mutual information could either be delayed or advanced at any other phase. We also observe an almost identical behavior when we input an amplitude modulated signal to the PSA. We are able to explain the physics of this ``fast-and-slow-light'' type of behavior utilizing a model assuming imbalanced gain on the positive and negative side bands. We obtain a good agreement between the experimental results and the theoretical simulations.