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 reason of enhanced state distinguishability. Here we show that 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 higher quantum efficiency compared with 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 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 with finite global squeezing. Therefore, with fixed finite squeezing, noisy but strongly discordant quantum states with a 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.
Highlights
In the context of quantum information and quantum technology the idea of reading classical data by means of quantum states arises quite naturally [1, 2]
The standard implementations of reading are based on optical technologies: the task is the readout of a digital optical memory, where information is stored by means of the optical properties of the memory cells that are in turn probed by shining light, e.g., a laser beam, on them
We have investigated Gaussian quantum reading protocols realized by weak optical sources in the worst-case scenario for quantum transmitters with respect to classical ones
Summary
In the context of quantum information and quantum technology the idea of reading classical data by means of quantum states arises quite naturally [1, 2]. For the quantum reading protocol with unitary coding, let us consider the maximum probability of error in distinguishing the output of a binary memory cell encoded using one identity and one arbitrary unitary channel WA chosen in the set of local unitary operations with non-degenerate harmonic spectrum. A maximum trace discord of response ( TRr = 1) implies that, irrespective of the coding, the maximally entangled transmitter will read any memory without errors: any local unitary operation with harmonic spectrum transforms a maximally entangled state into another maximally entangled state orthogonal to it, and yields perfect distinguishability at the output
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