Nonclassical readout of optical memories under local energy constraint

TL;DR

This paper investigates the advantage of nonclassical light in quantum reading of optical memories under a local energy constraint, identifying the critical number of modes needed for nonclassical sources to outperform classical ones.

Contribution

It introduces an analysis of quantum reading under a local energy constraint, contrasting with previous global energy constraint studies, and determines the mode threshold for quantum advantage.

Findings

Nonclassical light can outperform classical light in reading optical memories.

A critical number of signal modes is identified for quantum advantage.

The analysis shifts from a global to a local energy constraint framework.

Abstract

Nonclassical states of light play a central role in many quantum information protocols. Their quantum features have been exploited to improve the readout of information from digital memories, modelled as arrays of microscopic beam splitters [S. Pirandola, Phys. Rev. Lett. 106, 090504 (2011)]. In this model of "quantum reading", a nonclassical source of light with Einstein-Podolski-Rosen correlations has been proven to retrieve more information than any classical source. In particular, the quantum-classical comparison has been performed under a global energy constraint, i.e., by fixing the mean total number of photons irradiated over each memory cell. In this paper we provide an alternative analysis which is based on a local energy constraint, meaning that we fix the mean number of photons per signal mode irradiated over the memory cell. Under this assumption, we investigate the critical number of signal modes after which a nonclassical source of light is able to beat any classical source irradiating the same number of signals.