It is nontrivial to describe in theory the quantum behavior of a phase-sensitive heterodyne detector with a bichromatic local oscillator. On the one hand, a 3 dB noise penalty is expected for the detector due to the existence of an image band vacuum, which was assumed in a previous theoretical study. On the other hand, as a phase-sensitive device, the detector should be free of the 3 dB extra quantum noise, as verified by a recent experiment. However, the mechanism for the absence of the 3 dB noise penalty in the experimental observation remains unknown. To understand the relevant physics, we develop a comprehensive quantum theory, in agreement with experiment, for phase-sensitive heterodyne detection. This work should be important for us to understand the origin of the quantum noise in heterodyne detection. (C) 2016 Optical Society of America
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