Study On Quantum Velocity Limit For The Transport Process Of The Single Quantum Dot In Open Environment

Single quantum dot can be used as one of the important candidate materials for constructing the basic units of quantum computers because of it has the advantages of strong operability and easy preparation.The quantum computers operation efficiency is closely related to the information transmitted speed,so the speed of quantum state evolution is one of the main problems in the field of quantum information.Therefore,we choose quantum dots with unique quantum effects as the model to study the evolution of quantum states.Quantum Speed Limit defines the minimum time required for a quantum system evolve from the initial state to the final state.However,information transmission rate of the quantum dot system will be induced by the external environment,so it is an important assumption that how to weanken the external environment influence to improve the quantum information transmission efficiency at present.With the aim of improving the system evolution speed,the quantum velocity limit of single quantum dot transport system is studied under different environmental conditions.In order to study the quantum velocity limit time of the single quantum dot transport system,we derive the reduced density matrix of the system based on the quantum dot transport theory in the Open environment,and select the method of Bures Angle to quantify the geodesic distance between the initial and final states,and derive the expression of the acceleration ability of the transport system in the dissipative and pure dephasing environment.The quantum velocity limit time of the initial pure state and mixed state is plotted with the driving time.The influences of physical parameters for the Quantum Velocity Limit Time are given,such as tunneling probability,relaxation rate,decoherence rate and energy range.The theoretical results show that in the dissipative environment,different tunneling probabilities have different effects.The increase of left tunneling probability has a weak effect on the accelerating capability of the system,due to the Coulomb blocking effect and quantum coherence.On the other hand,the right tunneling probability has a significant Influence on the accelerating capability is promoted with the increase of right tunneling probability because of the effect of channel blocking and cotunneling effect.The Increase of energy displacement promotes the accelerating capability of the system and changes the oscillation frequency of the system,owing to its taking longer time for the system to evolve to a target state.The effect of the relaxation rate for the system’s accelerating capability is not monotonic,there is an interesting turning point due to the change of electron layout number.When the relaxation rate is less than this point,the accelerating capability of the system will oscillate.When the relaxation rate is higher than this point,the change of accelerating capability is monotonically suppressed by the relaxation rate.In general,the increase of the relaxation rate weakens the acceleration capability of the system.In the pure dephasing environment,the change of left-side tunneling probability has a more significant effect on the accelerating capability of the system than that in the dissipative environment.Compared with the improved influence of the right tunneling probability in the dissipative environment,the change of the accelerating capability in the pure dephasing environment shows a completely different suppression effect.The increase of pure phaseing rate weakens the acceleration space of the quantum system due to nonequilibrium property.The increase of the energy range will cause the evolution of the system to deviate from the geodesic path and promote the accelerating capability.The innovation of this thesis lies in introducing the quantum velocity limit theory into the transport model of quantum dot system,deducing the density matrix of the single quantum dot transport system and the expression of the system’s accelerating capability,analyzing the dynamics process under dissipative and pure dephasing environment,and discussing the effects of physical parameters such as tunneling probability,relaxation rate and energy range on the accelerating capability of state evolution,which provides a theoretical reference for the study of state evolution in quantum information.This thesis is divided into five chapters.The first chapter mainly introduces the research background and current situation of quantum velocity limit and the physical effects in the transport process of single quantum dot system.In Chapter 2,the development of quantum velocity limit boundary from closed system to open system is studied.At the same time,derive the quantum velocity limit based on absolute value inequality.In Chapter 3,we derive the density matrix of quantum dot transport system and then analyze the density matrix dynamics process and the acceleration ability in the dissipative environment.In the fourth chapter,we discuss the effects of parameters such as pure phasing rate and tunneling probability on the acceleration ability of the system in the environment of pure phasing.The fifth chapter is the summary of the work of this thesis and the prospect of future work.