Dephasing in coherent communication with weak signal states

Abstract

We analyze the ultimate quantum limit on the accessible information for an optical communication scheme when time bins carry coherent light pulses prepared in one of several orthogonal modes and the phase undergoes diffusion after each channel use. This scheme, an example of a quantum memory channel, can be viewed as noisy pulse position modulation (PPM) keying with phase fluctuations occurring between consecutive PPM symbols. We derive a general expression for the output states in the Fock basis and implement a numerical procedure to calculate the Holevo quantity. Using asymptotic properties of Toeplitz matrices, we also present an analytic expression for the Holevo quantity valid for very weak signals and sufficiently strong dephasing when the dominant contribution comes from the single-photon sector in the Hilbert space of signal states. Based on numerical results we conjecture an inequality for contributions to the Holevo quantity from multiphoton sectors which implies that in the asymptotic limit of weak signals, for arbitrarily small dephasing the accessible information scales linearly with the average number of photons contained in the pulse. Such behaviour presents a qualitative departure from the fully coherent case.

20 pages, final version

References in corpus (4)

• Influence of Atmospheric Turbulence on Optical Communications using Orbital Angular Momentum for Encoding
• Experimental demonstration of entanglement-enhanced classical communication over a quantum channel with correlated noise
• QPSK coherent state discrimination via a hybrid receiver
• Homodyne detection as a near-optimum receiver for phase-shift keyed binary communication in the presence of phase diffusion

Cited by in corpus (8)

• Optimized communication strategies with binary coherent states over phase noise channels
• Incoherent on-off keying with classical and non-classical light
• Squeezing-enhanced communication without a phase reference
• Phase noise in collective binary phase shift keying with Hadamard words
• Classical capacity per unit cost for quantum channels
• A robust hybrid receiver for binary phase-shift keying discrimination in the presence of phase noise
• Metrology-assisted entanglement distribution in noisy quantum networks
• Arithmetic Tuning of Dynamical Critical Exponents in Quasiperiodic Localization Transitions