Device-independent quantum reading and noise-assisted quantum transmitters

TL;DR

This paper demonstrates that noise can enhance quantum reading efficiency by leveraging discord of response in noisy quantum transmitters, outperforming classical and entangled states under certain conditions.

Contribution

It reveals that non-symmetric squeezed thermal states with high discord and noise imbalance can outperform classical and entangled transmitters in quantum reading.

Findings

Noisy squeezed thermal transmitters outperform coherent thermal states.

Quantum advantage increases with thermal noise due to discord of response.

Error probability vanishes asymptotically with increasing local thermal noise.

Abstract

In quantum reading, a quantum state of light (transmitter) is applied to read classical information. In the presence of noise or for sufficiently weak signals, quantum reading can outperform classical reading by enhanced state distinguishability. Here we show that the enhanced quantum efficiency depends on the presence in the transmitter of a particular type of quantum correlations, the discord of response. Different encodings and transmitters give rise to different levels of efficiency. Considering noisy quantum probes we show that squeezed thermal transmitters with non-symmetrically distributed noise among the field modes yield a higher quantum efficiency compared to coherent thermal quantum states. The noise-enhanced quantum advantage is a consequence of the discord of response being a non-decreasing function of increasing thermal noise under constant squeezing, a behavior that leads to an increased state distinguishability. We finally show that, for non-symmetric squeezed thermal states, the probability of error, as measured by the quantum Chernoff bound, vanishes asymptotically with increasing local thermal noise at finite global squeezing. Therefore, at fixed finite squeezing, noisy but strongly discordant quantum states with large noise imbalance between the field modes can outperform noisy classical resources as well as pure entangled transmitters with the same finite level of squeezing.