Research On Improvement Of Performance In Quantum Interferometry Based Upon Gaussian-state Engineering

Quantum interferometry can realize the signal detection at the photon level and is a technical means of precision measurements for weak signals.As a key metric to evaluate measurement performance,phase sensitivity in quantum interferometry has received a lot of attention.The theoretical limit,effect factors and improvement methods of phase sensitivity are the focus issues at home and abroad.This dissertation focuses on four aspects about phase sensitivity in quantum interferometry: the research on phase sensitivity limit,the research on intrinsic factors of phase sensitivity,the research on extrinsic factors of phase sensitivity,and the research on novel measurement methods of improving phase sensitivity.This dissertation first studies phase sensitivity limit.According to the theory of quantum parameter estimation,the relationship between phase sensitivity limit and measurement strategies is established.Regarding the measurement schemes without reference sources in the measurement strategy,a novel method based on phase-averaging approach is proposed to analyze and calculate the phase sensitivity limit,solving the problem that the phase sensitivity limits calculated from different phase-shift operators are different.Regarding the measurement schemes including reference sources in the measurement strategy,a novel method which can analyze and calculate the phase sensitivity limit is proposed by using a single-path phase-shift operator.The fact that squeezed vacuum states are the optimal single-mode inputs is proven,and the phase sensitivity can break through the Heisenberg limit.The intrinsic factors of phase sensitivity are studied.According to the theory of phase space,the effect of detection efficiency is studied via a fictitious beam splitter,the effects of dark counts and response-time delay are studied through the use of photon statistics and time statistics,and the effect of unbalanced beam splitters is studied using the transfer matrix.Further,the relationship between phase sensitivity and intrinsic factors is established.On the basis of the above theoretical research,this dissertation proposes a novel method to analyze and calculate phase sensitivity under the effects of detection efficiency,dark counts,response-time delay,and unbalanced beam splitters.The results indicate that the measurement scheme using a coherent state and balanced homodyne measurement is robust to all kinds of intrinsic factors,and the phase sensitivity approaches the shot-noise limit.These results provide theoretical guidance on the design of system parameters in the practical measurements.The extrinsic factors of phase sensitivity are studied.According to the theory of quantum open systems,the effects of photon loss and thermal photon noise are studied via a fictitious beam splitter coupled with environment field in vacuum states and in thermal states,and the effect of phase diffusion is studied by using the classical stochastic process.The relationship between phase sensitivity and extrinsic factors is established.On the basis of the above theoretical research,this dissertation proposes a novel method to analyze and calculate phase sensitivity under the effects of photon loss,thermal photon noise,and phase diffusion.The results show that the measurement scheme using a coherent state and balanced homodyne measurement is robust to all kinds of extrinsic factors,and the phase sensitivity approaches the shot-noise limit.These results provide a theoretical foundation for the related research of restraining the effects originating from extrinsic factors.Finally,the novel methods to improve the phase sensitivity are studied in this dissertation.By analyzing the measurement mechanism of the current measurement methods,the restrictions on the improvement of phase sensitivity are studied.Regarding the measurement methods based on nonlinear interferometers,a novel measurement method based on a hybrid interferometer is proposed,which utilizes a balanced beam splitter to replace the optical parametric amplifier.Regarding the measurement methods based on linear interferometers,a novel measurement method based on the assistance of a reference source is proposed,which uses the phase of local oscillator in balanced homodyne measurement as the benchmark of the measured phase.In addition,a novel measurement mechanism based on energy recycling is proposed;photons that are not measured at the output are reused.The results suggest that phase sensitivities of these three methods are improved and break through the shot-noise limit through the use of coherent states and balanced homodyne measurement.The improvement factors are 41.4%,41.4%,and 33.3%,respectively.The research in this dissertation improves the performance of quantum interferometry,which provides support for the development of quantum interferometry in the precision measurements of weak signals,and also for the application of quantum interferometry in the fields of biological tissue imaging,physical property analysis of solution,and photosensitive sample detection.