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Physical Review A

Enhancing the performance of quantum radar with zero-photon subtraction

ShengLi Zhang, Liangsheng Li, Maoxin Liu, JinChun Li, Wang Sun, QuanChun Yu

Published Feb 24, 2025• 6 citations
Publisher

Abstract

Quantum radar, also known as quantum illumination, is a type of quantum-sensing protocol for detecting noncooperative targets hidden in noisy environments. Recently, considerable research efforts have been focused on optimizing quantum illumination via conditional photon-detection methods, such as photon subtraction and photon catalysis of the entanglement source. However, to date, almost none of these studies have considered the probability of successful detection of nonzero photons. Often, the probability of conditional nonzero photon detection is extremely low, which may negate the advantage of conditional measurements in a quantum radar. In this paper, we propose enhancing the performance of quantum radars using zero-photon subtraction (ZPS), where no physical photons are subtracted from a given optical system. We demonstrate that the probability of ZPS is one or two orders of magnitude higher than that of nonzero photon detection. Our results show that ZPS helps enhance the performance of quantum radars, even when the probability of photon detection is considered. Moreover, in this paper, we consider a more realistic quantum radar in which target detection is performed using amplitude-damped quantum entanglement, which is more commonly used in the preparation of quantum entanglement in radar transmitters. This means that ZPS is a more efficient conditional photon-detection method for quantum illumination, providing a more robust scheme for developing future quantum radars.

DOI
10.1103/physreva.111.022627

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Quantum radar, also known as quantum illumination, is a type of quantum-sensing protocol for detecting noncooperative targets hidden in noisy environments. Recently, considerable research efforts have been focused on optimizing quantum illumination via conditional photon-detection methods, such as photon subtraction and photon catalysis of the entanglement source. However, to date, almost none of these studies have considered the probability of successful detection of nonzero photons. Often, the probability of conditional nonzero photon detection is extremely low, which may negate the advantage of conditional measurements in a quantum radar. In this paper, we propose enhancing the performance of quantum radars using zero-photon subtraction (ZPS), where no physical photons are subtracted from a given optical system. We demonstrate that the probability of ZPS is one or two orders of magnitude higher than that of nonzero photon detection. Our results show that ZPS helps enhance the performance of quantum radars, even when the probability of photon detection is considered. Moreover, in this paper, we consider a more realistic quantum radar in which target detection is performed using amplitude-damped quantum entanglement, which is more commonly used in the preparation of quantum entanglement in radar transmitters. This means that ZPS is a more efficient conditional photon-detection method for quantum illumination, providing a more robust scheme for developing future quantum radars.
Quantum radar systems leverage entangled photon pairs to detect and identify targets in noisy or cluttered environments with sensitivity beyond classical limits. By transmitting one photon of an entangled pair toward a distant object while retaining its partner locally, the system exploits quantum correlations to improve signal discrimination, reduce noise susceptibility, and enhance detection probability. This paper outlines the physical principles, operational architecture, and performance advantages of entanglement‑based illumination, providing a clear foundation for future quantum‑enhanced sensing technologies.(If you want it shorter, longer, or more formal, tap: shorter paragraph, longer paragraph, more formal)
There has been a great interest in quantum metrology (e.g., quantum interferometric radar) due to its applications in sub-Rayleigh ranging and remote sensing. Despite interferometric radar has received vast amount of attentions over the past two decades, very few researches has been conducted on another type of quantum radar: quantum illumination radar, or more precisely quantum target detection. It is, in general, used to interrogate whether the low-reflectivity target in a noisy thermal bath is existed using quantum light. The entanglement properties of its emitted light source give it a unique detection advantage over the classical radar. Entangled coherent state (ECS), as a class of quantum states with high entanglement robustness in noisy environments, has been widely used in several fields of quantum science such as quantum informatics, quantum metrology . In this paper, we investigate the target detection performance of quantum illumination radar based on three different types of ECS states. We employ the two-mode squeezed vacuum state (TMSV) and the coherent state as benchmarks to compare and analyze the relationship between the entanglement strength of the three types of ECS states and their quantum illumination detection performance. We found that the detection performance of the three ECS states is better than that of the coherent state. However, it is inferior to that of the TMSV state when the target is of low reflectivity. The emitted photon number is much smaller than the background noise (we call this as “good” illumination conditions). On the contrary, quantum illumination radar has no obvious advantage over coherent state radar for target detection under other illumination conditions; further, the detection performance of these three types of ECS states is not evidently related to that of the TMSV state and the coherent state. Finally, we reveal that the target detection performance of quantum illumination for the first two types of ECS states can be determined by their entanglement strength under “good” illumination conditions by adjusting the inter-modal phase of these two ECS states while keeping the emitted photon number constant. Under other illumination conditions, there is no evidence to demonstrate the entanglement strength of ECS states being associated with their target detection performance.
One of the major scientific thrusts from recent years has been to try to harness quantum phenomena to dramatically increase the performance of a wide variety of classical information processing devices. These advances in quantum information science have had a considerable impact on the development of standoff sensors such as quantum radar. In this paper we analyze the theoretical performance of low-brightness quantum radar that uses entangled photon states. We use the detection error probability as a measure of sensing performance and the interception error probability as a measure of stealthiness. We compare the performance of quantum radar against a coherent light sensor (such as lidar) and classical radar. In particular, we restrict our analysis to the performance of low-brightness standoff sensors operating in a noisy environment. We show that, compared to the two classical standoff sensing devices, quantum radar is stealthier, more resilient to jamming, and more accurate for the detection of low reflectivity targets.
Quantum radar based on the mechanism of quantum physics and the quantum information is a new sensing technology that was developed to solve technology bottleneck of classic radar. Especially, The Quantum illumination based on entanglement light beam could overcome noise and information loss. In this paper, the principle of quantum radar is introduced in detail, and the quantum illumination radar scheme using entangled photons is discussed. Then, target detection method based on entangled photons is given, and simulation results are showed. Finally, it is demonstrated by experiments that the performance of entangled photon detection system is superior to non-entangled photon detection system in a noisy and lossy environment, and the targets appear to look bigger when looked with low photon number.
Quantum radar uses the strong correlations of entangled photons and has a great potential to improve the detection sensitivity. Recently, many research results have been achieved in theoretical analysis and experiments on the performance advantages of quantum illumination radar. However, there are limited researches on its detection range. Based on the analysis of the noise tolerance of entangled state photons, we study the advantages of quantum illumination radar in detection range based on radar equation. It is shown that the detection range of quantum illumination radar is larger than that of classical radar in some regimes due to the strong noise suppression ability of quantum radar.
Quantum illumination is one of the most basic ways to realize the quantum radar for detection of low-reflectivity targets embedded in a thermal-noise bath. It preserves a strong advantage over the classical counterparts even though its fragile quantum entanglement is completely destroyed by a large amount of noise and losses. In this paper, we describe and analyze a discrete-variable quantum illumination system with ancillary degrees of freedom of entangled photon pairs. Comparing the error probability bound, i.e., the quantum Chernoff bound, we identify that this system indeed offers higher accuracy than the single-photon illumination and quantum illumination with single degree of freedom of entangled photon pairs. Furthermore, the utilization of ancillary degrees of freedom exponentially enhances signal-to-noise ratio over quantum illumination without ancillary degrees of freedom. It means that this system reduces the necessary amount of signal photons to accurately determine whether the object is present or absent in the target region, which is absolutely crucial to the stealthiness of the radar system.