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arXiv:2311.02016 · Physical Review A

Using random coherent states to mimic quantum illumination

Thomas Brougham, Nigam Samantaray, John Jeffers

Published Nov 3, 2023• 6 citations
arXivHTMLPDF

Abstract

Quantum illumination uses quantum correlations to provide an enhanced detection of an object in the presence of background noise. This advantage has been shown to exist even if one uses nonoptimal direct measurements on the two correlated modes. Here we present a protocol that mimics the behavior of quantum illumination, but does not use correlated or entangled modes. Instead, the protocol uses coherent (or phase-randomized coherent) pulses with randomly chosen intensities. The intensities are drawn from a distribution such that the average state looks thermal. Under appropriate conditions, the mimic protocol can perform similarly to quantum illumination schemes that use direct measurements. This holds even for a reflectance as low as ${10}^{\ensuremath{-}7}$. We also present an analytic condition which allows one to determine the sets of parameters in which each protocol works best.

DOI
10.1103/physreva.108.052404

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Quantum illumination uses quantum correlations to provide an enhanced detection of an object in the presence of background noise. This advantage has been shown to exist even if one uses nonoptimal direct measurements on the two correlated modes. Here we present a protocol that mimics the behavior of quantum illumination, but does not use correlated or entangled modes. Instead, the protocol uses coherent (or phase-randomized coherent) pulses with randomly chosen intensities. The intensities are drawn from a distribution such that the average state looks thermal. Under appropriate conditions, the mimic protocol can perform similarly to quantum illumination schemes that use direct measurements. This holds even for a reflectance as low as 10\ensuremath−7{10}^{\ensuremath{-}7}10\ensuremath−7. We also present an analytic condition which allows one to determine the sets of parameters in which each protocol works best.
Quantum illumination consists in shining quantum light on a target region immersed in a bright thermal bath with the aim of detecting the presence of a possible low-reflective object. If the signal is entangled with the receiver, then a suitable choice of the measurement offers a gain with respect to the optimal classical protocol employing coherent states. Here, we tackle this detection problem by using quantum estimation techniques to measure the reflectivity parameter of the object, showing an enhancement in the signal-to-noise ratio up to 3 dB with respect to the classical case when implementing only local measurements. Our approach employs the quantum Fisher information to provide an upper bound for the error probability, supplies the concrete estimator saturating the bound, and extends the quantum illumination protocol to non-Gaussian states. As an example, we show how Schrödinger's cat states may be used for quantum illumination.
Quantum illumination uses quantum correlations to improve the detection of objects in the presence of background noise. A simple and common practical approach to quantum illumination is to use threshold detectors to measure the idler mode. We investigate the optimization of these protocols. Surprisingly, we find that there can be an advantage to having a signal detector whose quantum efficiency is significantly less than perfect, one that does not vanish for low object reflectivities or signal strengths. We also show that decreasing the separation between pulses, while keeping the rate of photons transmitted per second fixed, can improve the performance, under appropriate conditions. We further show that postselecting on the idler detector firing is less efficient at object detection than not postselecting. Published by the American Physical Society 2024
Proofs of the quantum advantage available in imaging or detecting objects under quantum illumination can rely on optimal measurements without specifying what they are. We use the continuous-variable Gaussian quantum information formalism to show that quantum illumination is better for object detection compared with coherent states of the same mean photon number, even for simple direct photodetection. The advantage persists if signal energy and object reflectivity are low and background thermal noise is high. The advantage is even greater if we match signal beam detection probabilities rather than mean photon number. We perform all calculations with thermal states, even for non-Gaussian conditioned states with negative Wigner functions. We simulate repeated detection using a Monte-Carlo process that clearly shows the advantages obtainable.
Proofs of the quantum advantage available in imaging or detecting objects under quantum illumination can rely on optimal measurements without specifying what they are. We use the continuous-variable Gaussian quantum information formalism to show that quantum illumination is better for object detection compared with coherent states of the same mean photon number, even for simple direct photodetection. The advantage persists if signal energy and object reflectivity are low and background thermal noise is high. The advantage is even greater if we match signal beam detection probabilities rather than mean photon number. We perform all calculations with thermal states, even for non-Gaussian conditioned states with negative Wigner functions. We simulate repeated detection using a Monte-Carlo process that clearly shows the advantages obtainable.
Quantum illumination is a quantum sensing protocol primarily used for object detection, which aims to detect the presence of a target with low reflectivity in the free space using quantum light fields. Here we investigate a quantum illumination scheme using an entangled light source by performing non-Gaussian operations on the two-mode squeezed vacuum (TMSV) state in order to reduce the detection error probability and meanwhile improve the signal-to-noise (SNR) ratio. We demonstrate that under the same squeezing parameter, the non-Gaussian operations can significantly reduce the detection error rate compared with the original TMSV state. Under the same average signal photon number, both the TMSV states with and without non-Gaussian operations can provide smaller error rate than that of the coherent state. In addition, we consider the balanced homodyne detection on idler and return signal photons as joint measurement and find that non-Gaussian operations can enhance the SNR of target detection by about 6--9 dB compared with that using TMSV. These results here demonstrate the advantage of the non-Gaussian entangled source in quantum illumination protocol and can find potential applications in target detection in noisy environment.
Quantum-enhanced sensing has a goal of enhancing a parameter sensitivity with input quantum states, while quantum illumination has a goal of enhancing a target detection capability with input entangled states in a heavy noise environment. Here we propose a concatenation between quantum-enhanced sensing and quantum illumination that can take quantum advantage over the classical limit. First, phase sensing in an interferometry is connected to a target sensing via quantum Fisher information. Second, the target sensitivity is investigated in noisy quantum-enhanced sensing. Under the same input state energy, for example, NNN-photon entangled states can exhibit better performance than a two-mode squeezed vacuum state and a separable coherent state. Incorporating a photon-number difference measurement, finally, the noisy target sensitivity is connected to a signal-to-noise ratio which is associated with a minimum error probability of discriminating the presence and absence of the target. We show that both the target sensitivity and the signal-to-noise ratio can be enhanced with increasing thermal noise.