Phase Sensitive Amplification
We investigate the advance and delay of information transmitted through an optical phase-sensitive amplifier (PSA). We start with a two-mode entangled state created by four-wave mixing in hot 85Rb vapor and measure the mutual information shared by the two modes. 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. The cross-correlation between the two modes of a bipartite EPR state can be advanced by propagation through a fast-light medium [U. Vogl, et al., New J. Phys. 16, 013011 (2014)] and, the extra noise added by a phase-insensitive amplifier has been shown to limit the advance of entanglement, preventing the mutual information from traveling superluminally [J. B. Clark, et al., Nat. Photon. 8, 515 (2014)]. In the case of a PSA, however, it is well known that no extra noise will be added for the correct PSA phase (e.g. at the maximal amplification and the maximal deamplification). It is therefore of interest to examine the behavior of the dispersion and the mutual information when passing a signal through a PSA operated at different phases.
We hope to use nonclassical states of light to perform enhanced imaging of biological samples. Four-wave mixing in Rb vapor can produce beams of light with quantum correlations in their intensities. These correlations give rise to “intensity-difference squeezing” meaning that the uncertainty of the intensity difference of the two beams is smaller than possible with classical beams. This reduction of uncertainty, or noise, can lead to more precise optical measurements, including those used in imaging systems.
In this project, we attempt to directly measure intensity-difference squeezing of bright twin beams produced from four-wave mixing on an integrating CCD camera. The multi-mode nature of the four-wave mixing process allows for the production of images containing spatial correlations and entanglement which should be accessible with CCD measurement of the images. The first step is finding the optimum conditions for measuring low-frequency intensity difference squeezing and removing any technical noise and scattered light from the images. Being able to measure noise reduction in correlated images directly on a CCD camera will open up a range of applications for quantum-enhanced imaging using nonclassical light.