QAM Adaptive Measurements Feedback Quantum Receiver Performance

TL;DR

This paper analyzes the performance of adaptive measurement feedback quantum receivers for 16-QAM signals, considering realistic imperfections and detector capabilities, demonstrating potential quantum advantage with current technology.

Contribution

It provides a comprehensive theoretical study of adaptive quantum receivers for QAM, including effects of imperfections and the use of photon-number-resolving detectors, highlighting achievable gains.

Findings

PNRDs can mitigate effects of imperfections on error rate

Moderate stages of adaptive measurement provide quantum advantage

Current technology can achieve reasonable gain over SQL

Abstract

We theoretically study the quantum receivers with adaptive measurements feedback for discriminating quadrature amplitude modulation (QAM) coherent states in terms of average symbol error rate. For rectangular 16-QAM signal set, with different stages of adaptive measurements, the effects of realistic imperfection parameters including the sub-unity quantum efficiency and the dark counts of on-off detectors, as well as the transmittance of beam splitters and the mode mismatch factor between the signal and local oscillating fields on the symbol error rate are separately investigated through Monte Carlo simulations. Using photon-number-resolving detectors (PNRD) instead of on-off detectors, all the effects on the symbol error rate due to the above four imperfections can be suppressed in a certain degree. The finite resolution and PNR capability of PNRDs are also considered. We find that for currently available technology, the receiver shows a reasonable gain from the standard quantum limit (SQL) with moderate stages.