Abstract
We analyze the effect of phase fluctuations in an optical communication scheme based on collective detection of sequences of binary coherent state symbols using linear optics and photon counting. When the phase noise is absent, the scheme offers qualitatively improved nonlinear scaling of the spectral efficiency with the mean photon number in the low-power regime compared to individual detection. We show that this feature, providing a demonstration of superaddivitity of accessible information in classical communication over quantum channels, is preserved if random phases imprinted on transmitted symbols fluctuate around a reference fixed over the sequence length.
Highlights
Binary phase shift keying (BPSK) is a well established modulation format in optical comunication [1, 2]
For individual detection of BPSK symbols, the minimum discrimination error is given by the celebrated Helstrom bound and can be attained using the Dolinar receiver [3,4] based on photon counting and fast feed-forward operations
We demonstrate that the nonlinear scaling of spectral efficiency in the low-power regime is retained when individual BPSK symbols experience small phase fluctuations occurring around a reference locked over the sequence length
Summary
Binary phase shift keying (BPSK) is a well established modulation format in optical comunication [1, 2]. Because of orthogonality properties of Hadamard matrices, applying an appropriate linear-optics transformation to such Hadamard words maps them onto the pulse position modulation (PPM) format that is suitable for direct detection. This strategy can approach in the leading order the Holevo quantity when optimized over the sequence length [8, 9]. We demonstrate that the nonlinear scaling of spectral efficiency in the low-power regime is retained when individual BPSK symbols experience small phase fluctuations occurring around a reference locked over the sequence length.
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