Research On Detection Mode And Performance Enhancement Of Quantum Lidar

For the unique non-classical features of quantum states, quantum theory and technology have produced important potential applications. The mature quantum theory and technology have promoted the rapid development of quantum communication, quantum computation, quantum interference, metrology and sensors. The quantum key distribution(QKD) in free space has achieved initial successes and the Laser Interference Gravitational Wave Observation(LIGO) based on the theory of quantum metrology has been already realized. In this period, quantum sensing theory has been also gradually developed, which includes quantum radar, quantum pulse compression ladar, quantum enhanced ladar and quantum secured imaging lidar, and so on. Quantum lidar is an inter-discipline subject of quantum information theory and laser radar technology. Compared with the traditional lidar, quantum lidar has the advantages of anti-jamming, high sensitivity, high longitudinal and angular resolution, and has been attracting many attentions in the field of lidar. In this dissertation, the detection methods and performance enhancement of quantum lidar are investigated both theoretically and experimentally.Firstly, the modified system, called pseudorandom modulation quantum secured lidar(PMQSL), has been proposed. Its overall structure has been designed and all performances have been investigated. The ranging resolution and accuracy of the serial correlation based on pseudo-random codes are analyzed theoretically and the signal-to-noise ratio(SNR) is also derived at the same time. The security issues for ranging have been illustrated according to the BB84 protocol in QKD, which results in determining the threshold of error rate for secured ranging. It is shown that we can get the range accuracy of centimeter level when there are no jammers. However, the SNR and range accuracy will be descended in the presence of jammers, which reveals the jamming activity. The observed ranging accuracy of the proof-of-principle experiment is in agreement with the simulation value. The experimental results show that our system has a better ranging and anti-attack ability.The super-resolving quantum lidar scheme with the coherent superposition states(CSS) is investigated. This kind of lidar can be implemented with the photon-number-resolving detectors or the quantum homodyne detection, its sensitivity can achieve to the shot noise limit(SNL) and its resolution is much higher than the Rayleigh diffraction limit. The output signals and their sensitivity based on the intensity detection and the projection detection have been also derived. The lowdown of the super-resolving power of CSS has been in-depth analysis and detailed discussion. In addition, the effects of photon loss and phase noise on the overall performance of our scheme are further studied. The binary-outcome parity and zero-nonzero(i.e., the so called Z-detection or on-off detection) photon counting measurements are introduced to enhance the resolution and sensitivity. The effects of phase noise on the output signal are considered in the calculation according to the master equation. The results show that coherent states cannot show any enhanced sensitivity and resolution relative to that of even coherent states in real environments.We propose a unified description to the scheme of the entangled coherent-state quantum lidar by utilizing the general expression of the conditional probabilities for detecting a binary outcome in photon counting measurement. We first have derived out the conditional probabilities and the average value of detecting an outcome with the parity photon counting measurement. By the numerical calculation, our scheme shows N-fold super-resolution, i.e., beating the Rayleigh diffraction limit. The resolution of our scheme with parity detection is N( N) times enhanced relative to that of the coherent-state strategy with the same(intensity) detection, where N is the average number of photons. Afterwards, we investigate the relationship of the resolution and the best sensitivity against the photon loss rate. Secondly, we focus on the roles of the phase noise on the resolution and sensitivity on the detection performance according to the master equation. Finally, the zero-nonzero counting shows worse sensitivity than those of the parity detection, which is just opposite from the case as demonstrated in the recent coherent-light Mach-Zehnder experiment and theory.In the end, the optimal detection methods of quantum lidar with coherent states in the presence of photon loss and phase noise have been investigated. Taylor series is exploited to directly expand the interference signals to separate the detected phase and the phase noise produced by the phase diffusion process. According to this operation, the expressions of the interference signal and their sensitivity are analytically illustrated by binary outcome homodyne detection, parity photon counting measurement and zero-nonzero photon counting measurement. These expressions show that phase noise and photon loss degrade the coherence of the interference signal, and further decay the system performance. The numerical results demonstrate that homodyne detection possesses the best sensitivity and resolution in the diffusion region of 2κ10-<, parity detection shows the best resolution and zero-nonzero detection indicates the optimal sensitivity in the rest region. In addition, zero-nonzero detection produces better sensitivity than parity detection both in the presence and absence of loss and noise.