The Dynamics Of Electron Transport In Open Double Quantum Dot Systems

In the past 30 years,with the rapid development of Micro experimental technique,one has been able to prepare semiconductor devices with nanoscale.The improvements of theory of quantum dynamics allow us to study the electrons transfer in components from a microscopic perspective.As the most representative basic concept in quantum effect,quantum coherence is increasingly regarded as an important resource due to its relevance that break thought the space,and has been widely applied in quantum information processing and quantum computing.In reality,this fragile physical resource is vulnerable to the interference of external environment to generate decoherence.The existence of outside observers would lead to the collapse of the wave function,which indirectly loses the quantum coherence in the process of observing the quantum system.Therefore,the research on the open quantum system is conducive to the understanding of the basic problems of quantum mechanics and the phenomenon of decoherence in quantum transport and measurement,which could provide theoretical support for the preparation of micro-electronic devices based on quantum dots and nanometers,and is of great significance to improve the accuracy of information transmission in quantum communication.When we study the transport and measurement problems of open quantum systems,the environment has two kinds of effects on the system: relaxation and dephasing.In order to facilitate the processing of environmental effects,the relaxation rate and the dephasing rate are presented in the form of constants in theoretical studies.But in rigorous terms,a more accurate way should be adopted to describe the environmental model of open quantum system because the environmental effect cannot be invariable.Since the establishment of stochastic fluctuation theory based on spectral diffusion,it has been widely used in the establishment of physical model and signal processing.Considering stochastic fluctuation model of environment,which can really reflect the environmental effect in quantum system decoherence effect.The environmental effect follows the distribution of noise statistical characteristics satisfying the specific function,and the Hamiltonian of the quantum system is generated by the coupling of the environment and the system.The state function describing the random process is given to reflect some statistical characteristics of the environmental noise,so as to accurately describe the dynamical evolution process of the environment on the system.According to this theory,starting from the time-convolutionless master equation,this paper considers the stochastic fluctuation model of the Gaussian white noise environment.The coupling between the system and the environment would cause the Hamiltonian of the system to generate fluctuation,and determines that this fluctuation meets the statistical characteristics of the OU type Gaussian white noise.The exact dynamical evolution equation of the interaction between the double quantum dot system and Gaussian white noise environment is derived.On this basis,we consider the measurement effect of the quantum point contact detector.The average current,Fano factor and average waiting time of the detector for different conditions are calculated by the full counting statistical theory and the method of additional Bloch vector that reflect the electron transfer properties in the double quantum dot.The theoretical results show that both the detector measurements and the Gaussian white noise environment have significant influence on the evolution of system dynamics under the long time limit.Measurement would enhance the localization of the quantum system and the average current and the Fano factor widen significantly with the changes of the level displacement due to the interaction with Gaussian white noise.The Fano factor presents an obvious super-Poissonian distribution,which is mainly caused by the quantum coherence and the cotunneling effect.In the short time limit,the measurements would accelerate the movement of the single electron in the detector and enhances the localization of the electron in the quantum dot.The presence of Gaussian white noise would inhibit the single electron transfer in the detector and destroy the unimodal structure of the average waiting time.The innovation of this paper lies in the theoretical derivation of the exact dynamical evolution equation of an open quantum system under the influence of the Gaussian white noise.Based on the theory of quantum measurement,we study the effects of the Gaussian white noise and quantum point contact measurement on the electron transfer in double quantum dot through the detector output,and analyze the noise parameters to extract the effective environmental information.Our researches provide theoretical reference to reduce the coherence loss caused by the environment for quantum experiment.Through studying detector external output Gaussian white noise environment and quantum point contact measurement of double quantum dot inside the influence of electron transfer,and analysis of noise parameters on this and to extract the effective environmental information,reduce the external environment for the quantum experiments coherence loss to provide theoretical reference.This paper mainly carries out relevant research on the dynamical properties of open quantum system under the influence of Gaussian white noise environment from five parts,focusing on the measurement caused by the detector and the fluctuation caused by the noise environment act on the dynamical evolution of the system.The content of this paper is arranged as follows:The first chapter is a review of this paper,which mainly introduces the transport and measurement theory based on the double quantum dot system,and briefly reviews the research status and latest progress on the dynamical evolution of open quantum systems.Meanwhile,the basic theoretical model of double quantum dot and quantum point contact detector are described in detail.The Hamiltonian form of the stochastic fluctuation environment model adopted in this paper and the high-order tunneling process are also presented.The second chapter is the theoretical basis of this paper,and introduces the theoretical framework of this paper in detail,including two kinds of quantum master equations of time-convolution and time-convolutionless,as well as the noise characteristics of Gaussian white noise.The full counting statistical theory of quantum transport process and the method of additional Bloch vector are described,and the calculation method of detector average current,Fano factor and average waiting time based on this theory are established.The third chapter is the derivation of the dynamical equation of the coupling system with the stochastic fluctuation environment.Based on the time-convolutionless quantum master equation,we derive the exact dynamical evolution equation of the interaction between the system and the Gaussian white noise environment,and give the second-order cumulative moment of the system fluctuation caused by the environment.Finally,the particle-number-resolved quantum master equation of the open system measured by the detector is deduced.The fourth chapter is the result analysis part of this paper.Because of the interference of detector and environment,the process of electron transport is affected and shows the particular transfer characteristic.We study the dynamical evolution of the interaction between the double quantum dot system and the Gaussian white noise environment,analyze the effects of the transverse and longitudinal noises caused by the fluctuating environment and the detector measurement on the average current and the Fano factor in the long time limit.Meanwhile,the relationship between the average waiting time of electron transfer in the detector and the noise environment is discussed.We give a reasonable explanation of the physical phenomena in the dynamical evolution of open quantum system.The fifth chapter is the summary and prospect of this paper.We summarize the work of the previous chapters,make a plan of the research work to be carried out in the future.