Quantum receivers with squeezing and photon-number-resolving detectors

TL;DR

This paper introduces quantum receivers utilizing squeezing and photon-number-resolving detectors to improve the discrimination of four-phase coherent states, achieving lower error rates and better dark count suppression than previous methods.

Contribution

It presents two novel receiver designs with squeezing and PNRDs, demonstrating their advantages over prior schemes in quantum state discrimination.

Findings

PNRD-based receiver achieves lower error rates.

Both receivers outperform previous schemes.

PNRD receiver suppresses dark count errors.

Abstract

We propose quantum receivers with optical squeezing and photon-number-resolving detector (PNRD) for the near-optimal discrimination of quaternary phase-shift-keyed coherent state signals. The basic scheme is similar to the previous proposals (e.g. Phys. Rev. A 84, 042328 (2012)) in which displacement operations, on-off detectors, and electrical feedforward operations were used. Here we study two types of receivers where one installs optical squeezings and the other uses PNRDs instead of on-off detectors. We show that both receivers can attain lower error rates than that by the previous scheme and in particular, the PNRD based receiver has a significant gain under the fixed number of feedfoward steps. Moreover, we show that the PNRD based receiver can suppress the errors due to dark counts, which is not possible by the on-off detector based receiver with a limited number of feedforwards.