Optical Properties of a Quantum-Noise-Limited Phase-Sensitive Amplifier based on Four-Wave Mixing in 85Rb Atomic Vapor

I will talk about our investigations on the optical properties of a quantum-noise-limited phase-sensitive amplifier (PSA). The PSA is implemented using four-wave mixing in hot 85Rb vapor based on a double-lambda atomic scheme. For the first part, I will talk about the PSA’s ability to pre-amplify quantum correlations in a two-mode squeezed state 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. For the second part, I will talk about the propagation of the quantum mutual information through a PSA. It has been demonstrated that the cross-correlation between the two modes of a bipartite entangled state can be advanced by propagation through a phase-insensitive, gain-assisted, fast-light medium. The extra noise added by the medium has been speculated to be the mechanism that limits the advance of entanglement, preventing the mutual information from traveling superluminally. In the case of the phase-sensitive amplification, 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 upper and lower frequency side bands. We obtain a good agreement between the experimental results and the theoretical simulations.