Multichannel optimal squeezing-displacement feedforward receiver with realistic photon-number-resolving detectors

This paper proposes a multichannel optimal squeezing-displacement receiver (MOSDR) with photon-number-resolving detectors for discriminating binary phase-shift keying (BPSK) coherent states. Unlike previous squeezing-based receivers whose gain is largely limited to the low photon-number regime, we partition the input signal into multiple channels so that the mean photon number in each channel is reduced, allowing the squeezing operation to be used more effectively in its favorable operating region. In addition, we use displacement feedforward between channels and accumulate the per-channel discrimination outcomes through a sequential decision process, thereby reducing the overall error probability. We analyze MOSDR under an ideal detector as well as under quantum efficiency, dark counts and visibility reduction. The results show that MOSDR outperforms an optimized-displacement multichannel displacement feedforward receiver and remains below the standard quantum limit over a wide photon-number range, exhibiting improved robustness to detection imperfections.