Performance of Coherent Frequency-Shift Keying for Classical Communication \\ on Quantum Channels

TL;DR

This paper evaluates the performance of coherent frequency-shift keying (CFSK) on quantum channels, revealing the sub-optimality of the square-root-measurement and proposing a more efficient discretized CFSK alphabet with improved rate performance.

Contribution

It demonstrates the sub-optimality of SRM for CFSK discrimination and introduces a discretized CFSK alphabet with higher mode efficiency and comparable error rates.

Findings

SRM is sub-optimal for CFSK state discrimination

Discretized CFSK achieves higher mode efficiency

Tradeoff between error probability and mode efficiency

Abstract

We evaluate the performance of coherent frequency-shift keying (CFSK) alphabets for communication on quantum channels. We show that, contrarily to what previously thought, the square-root-measurement (SRM) is sub-optimal for discriminating CFSK states. Furthermore, we compute the maximum information transmission rate of the CFSK alphabet, observing that it employs at least as many frequency modes as the signal states, and compare it with standard phase-shift-keying. Finally, we introduce a discretized CFSK alphabet with higher mode-efficiency, exhibiting comparable error-probability performance with respect to CFSK and better rate performance. Our results suggest the existence of a tradeoff between the CFSK reduced error-probability and its mode efficiency.