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.
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.
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.
There has been much recent interest in quantum metrology for applications to sub-Raleigh ranging and remote sensing such as in quantum radar. For quantum radar, atmospheric absorption and diffraction rapidly degrades any actively transmitted quantum states of light, such as N00N states, so that for this high-loss regime the optimal strategy is to transmit coherent states of light, which suffer no worse loss than the linear Beer's law for classical radar attenuation, and which provide sensitivity at the shot-noise limit in the returned power. We show that coherent radar radiation sources, coupled with a quantum homodyne detection scheme, provide both longitudinal and angular super-resolution much below the Rayleigh diffraction limit, with sensitivity at shot-noise in terms of the detected photon power. Our approach provides a template for the development of a complete super-resolving quantum radar system with currently available technology.
Quantum Sensors like Quantum Radar and Lidar based on the interference of non-classical states can achieve super-sensitivity beyond the Standard Quantum Limit (SQL). But as the photons transporting in atmosphere, the environmental interaction causes quantum de-coherence and results in the reduction of super-sensitivity range of the quantum sensors. The most significant effect of atmospheric transmission is photon loss along with phase fluctuation. In this letter, we introduce both the photon loss and phase fluctuation by adding a fictitious beam splitter in the signal arm of Mach- Zehnder interferometer (MZI). The density matrix with N00N and M&M' entangled states being the input states under the condition of photon loss and phase fluctuation is given respectively. Then as the optimal detection schemes parity operator is used as the detector and the formula of the sensitivity is derived. The super-sensitivity range of M&M’ and N00N states with de-coherence are simulated. As a consequence, with high photon loss M&M’ states shows the better phase sensitivity than N00N states but the N00N state is better when the loss is smaller than 20%. And with pure phase fluctuations N00N states get the longer range. M&M’ states is sensitive to the transmittance difference between two arms of the interferometer.
There has been much recent interest in quantum optical interferometry for applications to metrology, subwavelength imaging, and remote sensing such as in quantum laser radar (LADAR). For quantum LADAR, atmospheric absorption rapidly degrades any quantum state of light, so that for high-photon loss the optimal strategy is to transmit coherent states of light, which suffer no worse loss than the Beer law for classical optical attenuation, and which provides sensitivity at the shot-noise limit. We show that coherent light coupled with photon-number-resolving detectors can provide a super-resolution much below the Rayleigh diffraction limit, with sensitivity no worse than shot noise in terms of the detected photon power.
One important problem in quantum optics is to resolve an extremely small change of phase shift. The complementarity between photon number and phase sets an ultimate limit, the so-called Heisenberg limit, on the phase measurement sensitivity. The precise phase estimation has many technological applications, such as optical gyroscopes, gravitational wave detection, quantum imaging and sensing. In this thesis I show that the utilization of the parity measurement in the optical interferometry is actually applicable to a wide range of quantum entangled input states. Comparison of the performance of the various quantum states then can be made within such a unified output measurement scheme. Based on such a universal detection scheme, we present a comparison of the phase sensitivity reduction for various quantum states of light in the presence of photon loss. I also provide a simple condition that could be used to check whether an arbitrary state can achieve the Heisenberg limit independently of the detection scheme. It implies that the fidelity between the two output states with zero phase and minimal detectable phase applied respectively should significantly different from unity as the minimal phase shift scaling as 1/N, whereas the average number of input photons N goes to infinity. Next I give several measures to characterize the which-way information in the interference experiment. We define a new distinguishability associated with the fidelity between two density matrices to measure the which-way information. We demonstrate that the changes of mutual entropy as well as the entanglement of formation of the whole system, i.e. the physical system plus the which-way detector can also be used to describe the which-way information. With such quantities, we show that as the fringe visibility of the interference pattern gets larger, the less which-way information is obtained. Finally, I show that coherent light coupled with photon number resolving detectors can provide a super-resolution much below the Rayleigh diffraction limit, with sensitivity no worse than shot-noise in terms of the detected photon power. This scheme would have applications to laser radar, given the difficulty in making entangled states of light, as well as their susceptibility to atmospheric absorption.
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.