A quantum entangled radar uses entangled photons instead of separate photons. It has been shown that for quantum entangled interferometers that the value of quantum entanglement deteriorates in an environment with attenuation. This paper introduces a correction method that allows the quantum radar to maintain excellent performance even when dealing with an environment with attenuation. The correction method is analogous to techniques used in adaptive optics to improve images. Correction approaches based on signal sources deliberately introduced into the environment and electromagnetic sources already present in the environment are considered. Closed form expressions for estimating the range error are derived for the cases when the radar uses N entangled photons for imaging or N separate imaging photons. Simulations of radar range error estimates for entangled and separate photon cases for propagation media with widely varying attenuation properties are provided. Comparisons of estimates with and without atmospheric correction are given. The atmospheric correction method extends the range of the beneficial effects of entanglement by a factor of 82, i.e. to 5000 km for a slowly varying propagation medium. For a propagation medium with 50 times as much variation, the atmospheric correction method offers super sensitivity for three times the range of the uncorrected case.
A quantum entangled radar uses entangled photons instead of separate photons. It has been shown that for quantum entangled interferometers that the value of quantum entanglement deteriorates in an environment with attenuation. This paper introduces a correction method that allows the quantum radar to maintain excellent performance even when dealing with an environment with attenuation. The correction method is analogous to techniques used in adaptive optics to improve images. Correction approaches based on signal sources deliberately introduced into the environment and electromagnetic sources already present in the environment are considered. Closed form expressions for estimating the range error are derived for the cases when the radar uses N entangled photons for imaging or N separate imaging photons. Simulations of radar range error estimates for entangled and separate photon cases for propagation media with widely varying attenuation properties are provided. Comparisons of estimates with and without atmospheric correction are given. The atmospheric correction method extends the range of the beneficial effects of entanglement by a factor of 82, i.e. to 5000 km for a slowly varying propagation medium. For a propagation medium with 50 times as much variation, the atmospheric correction method offers super sensitivity for three times the range of the uncorrected case.
The entangled quantum radar applies the quantum information technology to the radar sensing network and detection system. The dynamic particle changes and optical attenuation caused by complex atmospheric environments will severely limit the traditional radar performance. Due to entanglement characteristics, the entangled optical quantum radar has better anti-stealth interference ability, stronger anti-turbulence properties, and higher spatial resolution which makes it promising in complex and high-attenuation environments. In addition, quantum radar based on the entangled light source can overcome the limitations of low imaging resolution and low confidentiality in traditional target detection. Therefore, high-precision positioning and high-resolution imaging are the research focus of the quantum radar sensing network. Based on this, we first design and optimize an optical path structure of the quantum entangled light source to obtain higher brightness entangled source which is suitable for complex atmospheric environments. Second, in response to the problem of low positioning accuracy in the traditional quantum radar, we design a new positioning optical path and propose a novel entangled optical quantum positioning method based on the photon scattering model. Third, to address the problems of low resolution and slow speed in traditional quantum radar imaging, we propose a new entangled light quantum imaging method based on two-phase coincidence counting. Finally, we conduct extensive experiments to evaluate the effectiveness of the proposed method in complex atmospheric environments and further provide possibilities for the entangled light source quantum radar sensing network.
The quantum illumination radar uses pairs of entangled photons to enhance the detection sensitivity of a reflecting target.In this paper, we worked on a quantum illumination radar using a pair of entangled photons in polarization in the microwave frequency range in the atmosphere.We studied the quantum information evolution modeling the propagation of a photon in the atmosphere while building two binary decision strategies for the QI radar.We focused on the quantum information evolution showing that the quantum discord representing quantum correlations beyond entanglement could represent an interesting resource to explore for the subject of quantum radar.In addition, we made an approximative estimation of the entanglement survival distance in the atmosphere.Results showed that an optimization should be found to favour the survival of quantum correlations or the signal-to-noise ratios calculated with the binary decision strategy.
This article presents a comprehensive analysis of two classes of quantum radars, including quantum direct-detection and quantum-entangled noise radars. In the first case, inspired by the well-established concept of single-photon LiDARs, we investigated the performance of single-photon radars, in which state-of-the-art single microwave-photon detectors are employed to enhance the detection sensitivity and enable the detection of weaker signals. We derived analytical expressions for the maximum detection range of both classes of quantum radars in terms of the Lambert W function, by considering all relevant system, target, and environmental parameters. Our formulation facilitates direct comparison of noise radars with direct-detection radars and suggests that a quantum-entangled noise radar can be regarded as an enhanced direct-detection radar with an effective threshold signal-to-noise ratio. Furthermore, we applied this framework to classical-correlated noise radars and defined the parameter range enhancement factor (REF) to quantify the superiority of quantum-entangled noise radars over their classical counterparts. Moreover, we introduced a rule-of-thumb for approximating the REF. We also examined the influence of limitations imposed by various microwave detection technologies. Our analysis shows that the conventional antennas limit the potential benefits of quantum-entangled noise radar systems. We also demonstrated that the optimal detection method for these radars is a microwave detector based on a quantum transducer combined with a single optical-photon detector. We showed that, with the current technology, implementing a quantum-entangled noise radar with the maximum detection range on the order of few kilometers is possible. Finally, we explored the potential applications of quantum-entangled noise radars.
There has been aroused much interest in quantum metrology such as quantum radar, due to its applications in sub-Raleigh ranging and remote sensing. For quantum radar, the atmospheric absorption and diffraction rapidly degrade any actively transmitted quantum states of light, such as N00N and MM' states. Thus for the high-loss condition, the optimal strategy is to transmit coherent state of light, which can only provide sensitivity at the shot-noise limit but suffer no worse loss than the linear Beer's law for classical radar attenuation. In this paper, the target detection theory of quantum interferometric radar in the presence of photon loss is thoroughly investigated with the model of Mach-Zehnder interferometer, and the dynamic evolution of the quantum light field in the detecting process is also investigated. We utilize the parity operator to detect the return signal of quantum interferometric radar with coherent-state source. Then we compare the detection result of quantum radar with that of classical radar, which proves that the quantum radar scheme that employs coherent radiation sources and parity operator detection can provide an N-fold super-resolution, which is much below the Rayleigh diffraction limit; besides, the sensitivity of this scheme can also achieve the shot-noise-limit. Also, we analyze the effect of atmospheric attenuation on the performance of quantum radar, and find that the sensitivity is seriously influenced by atmospheric attenuation:only when the reference beam and the detection beam have the same transmissivity, will the sensitivity increase monotonically with increasing the photon number per pulse N, otherwise it first increases and then decreases with increasing N. Further, the sensivity is directly proportional to 1/N for the first case. In conclusion, we investigate the effects of atmospheric absorption on the resolution and sensitivity of quantum radar, and find that one can overcome the harmful effects of atmospheric attenuation by adjusting the transmissivity of reference beam to the atmospheric transmittance.
In this study, some important parts of a quantum radar are designed using the quantum electrodynamics theory and significantly focused on entanglement conservation. Quantum radar is generally defined as a detection sensor that utilizes the microwave photons like a classical radar and simultaneously employs quantum phenomena to improve detection, identification, and resolution capabilities. However, the entanglement is so fragile, unstable, and difficult to preserve for a long time. Also, more importantly, the entangled states have a tendency to leak away due to the noise. The points mentioned enforces that the entangled states should be carefully studied at each step of the quantum radar detection processes such as the creation of the entangled photons in the tripartite system, the amplification of the photons, the propagation into the atmosphere, and the reflection from the target. At each step, the parameters related to the real mediums and target material can affect the entangled states to leak away easily. The results of simulations indicate that the features of the tripartite system and amplifier are so important to lead the detected photons to remain entangled with the optical modes. Nonetheless, it is found that a lot of entangled photons lose the related non-classical correlation.
Much interest has been aroused in quantum metrology such as quantum interferometric radar, due to its application in sub-Raleigh ranging and remote sensing. Generally, the quantum signal emitted by quantum radar will be affected by atmosphere medium. For instance, both atmospheric loss and atmospheric scintillation seriously affect the sensitivity and resolution of quantum radar. In fact, the effects of atmospheric loss on the sensitivity and resolution of quantum interferometric radar have been investigated thoroughly and completely in the past decades. However, the investigation about the influence of atmospheric scintillation is lacking until now. To realize practical quantum interferometric radar, the perturbation coming from turbulent atmosphere must be considered, thus it is necessary to investigate how the atmospheric scintillation affects the performance of quantum radar.In this paper, the influence of intensity fluctuation which is caused by atmospheric scintillation on the performance of quantum interferometric radar with entangled coherent states (ECS) is thoroughly investigated. We first introduce the physical model of quantum interferometric radar, and the dynamic evolution of quantum light field in atmosphere is obtained by solving the master equation of dissipation channel. Considering the dissipation and fluctuation caused by atmospheric scintillation, we regard the turbulent atmosphere as so-called dissipation-fluctuation channel. Moreover, according to classical statistical theory of turbulence, we derive the explicit expression of probability distribution of transmission coefficient P(T), this probability distribution of transmission cofficient, which is determined by average transmission coefficient TD and scintillation index βD2 plays a crucial role in the studying of atmospheric scintillation.The results of investigation show that atmospheric scintillation leads to the degradation of the sensitivity and resolution of ECS quantum interferometric radar at lower atmospheric loss. Under the higher lossy condition of atmosphere, atmospheric scintillation can greatly enhance the performance of quantum interferometric radar. Furthermore, the critical atmospheric transmission coefficient which determines the lower and higher loss of atmosphere keeps increasing with the increase of average photon number per pulse. Increasing the atmospheric scintillation, rather than introducing noise and degrading the performance of quantum radar, can improve the sensitivity and resolution.This anomalous phenomenon can be explained only by quantum decoherence theory. As is well known, the supersensitivity and super-resolution of quantum radar are based on the nonlocal characteristic of quantum light field, while the dissipation process will induce decoherence that leads to the loss of nonlocal characteristic, and finally degrades the performance of quantum radar. However, there have been several researches indicating that the dissipation-fluctuation channel can alleviate the decoherence effect and maintain the nonlocal characteristic of quantum light field compared with pure dissipation channel. For the evolution of quantum light field in dissipation medium, the loss of amplitude plays a crucial role at a lower loss, while the decoherence will play a dominant role at a higher loss. Consequently, the fluctuation may induce extra noise and degrade the performance of quantum radar at lower loss. For higher loss, the fluctuation can prevent the decoherence process and maintain the quantum characteristic of light field, thus the atmospheric scintillation finally improves the sensitivity and resolution of quantum radar.