Theoretical Studies Of Optomechanical Systems On Quantum Signal Processing

Quantum mechanics is widely used to study microscopic particles.Since its creation,it has been revealing the microscopic world profoundly,promoting the development of modern technology,and inducing the prosperity in the semiconductor industry.In the past forty years,the research on quantum mechanics has entered a new stage,meanwhile quantum information and quantum computing have become the current research hot domain.For establishing quan-tum information networks and manufacturing quantum computers,signals need to be controlled and protected from the environment.Therefore,it is especially important for signal control and quantum noise suppression.Optomechanical system plays an important role in transmitting and controlling optical fields.The mechanical oscillator in the optomechanical system can sense sig-nals such as weak force,acceleration,and tiny mass change.These signals can be detected by converting them to optical fields.In addition,the coupling of the oscillator and electromagnetic field is not limited by the frequency of field,so the optomechanical system can also be used as a microwave detector where mechanical oscillator both couples to the microwave and optical field.To treat the problems of signal output and noise suppression,the theory of open quantum system is involved.This thesis will focus on the theoretical study of quantum signal processing by optomechanical system under the open quantum system regime.The specific contents are as follows:Optomechanical system coupling to fibers constitutes a multi-ports quantum router.Through calculation,we find that there are strong nonlinear interactions between the quasi-mode and the mechanical oscillator in the two coupled optomechanical systems.With this nonlinear inter-action,the photon anti-bunching effect can be achieved,and it results in single photon states.Based on the single photon nonlinearity and the multi-port output,we have proposed a theoret-ical scheme for a multi-ports single photon router.The coupling of the optomechanical system to its environment may be nonlinear.With two nanospheres which are trapped by optical field(equivalent to mechanical oscillator),we studied the dynamics of two trapped nanospheres which linearly and nonlinearly couple to their environment,when the trapping field does not satisfy the single mode approximation,but has finite frequency width.The master equation is deduced as well.The influence of nonlinear coupling on non-Markovianity was studied.We found that the nonlinear coupling improves the non-Markovianity of system.In terms of signal sensing,we studied the application of optomechanical system in mi-crowave detection,where the oscillator coupling to non-Markovian reservoirs is considered.By comparing different environment spectra,we found that the effective frequency of the oscil-lator is shifted significantly,and the sensitivity is improved,when the spectrum is super-Ohmic.Finally,we propose a remote weak signal detection scheme which is based on optomechanical system.Coupled cavity array is used to transmit the optical field.It can be equivalent to a structured reservoir which is shared between sensing and observing cavity.We studied the con-ditions for the occurrence of bound states in strong non-Markovian case.With optimized bound states,the linearized optomechanical coupling can be effectively improved,and the signal can be transmitted without loss.Therefore,the sensitivity of the remote detector can be improved.These theoretical studies can be useful for optomechanical system as a quantum signal processing platform,and provide theoretical background for relevant experimental research.