Theoretical Realization Of Quantum Dense Coding In A Spin Chain Under Dissipative Environment With Memory

Any real quantum system inevitably interacts with the external environment,causing the quantum system to decoherence.To study the decoherence properties and dynamic behavior of open quantum systems,it is necessary to consider the characteristics of their environment.Different types of environments may lead to completely different kinetic results.The traditional methods of dealing with open quantum systems often only consider the weak coupling between the system and the environment,and regard the environment as a Markov environment without memory.However,under the condition that the system is strongly coupled with the environment,the non-Markov effect generated by the memory feedback of the environment must be considered.Therefore,studying the non-Markov dynamics and related feedback control of open quantum systems has important theoretical and practical significance.As we all know,the most attractive property of quantum mechanics is quantum entanglement.In recent years,quantum entanglement has been extensively studied because it plays an important role in quantum information processing,such as quantum dense coding,quantum teleportation,and quantum key distribution.Quantum dense coding is realized by means of quantum entangled states,and it is one of the most popular topics in quantum information.The system discussed in this paper is an open quantum system.According to the characteristics of the environment,the evolution of the open quantum system can be divided into two basic processes,namely Markovian and non-Markovian.This paper mainly studies the theoretical implementation of quantum dense coding in the Heisenberg XXZ model and the Heisenberg XX model in non-Markov environment.In this thesis,the non-Markov quantum state diffusion(Quantum State Diffusion)method is used to deal with the precise dynamic evolution of open quantum systems without the influence of coupling strength,correlation time and library spectral density.It numerically processes a random pure state,which can greatly improve the calculation efficiency and is suitable for processing more complex models.The paper is divided into four chapters.The first chapter briefly introduces the development of quantum information theory and some basic knowledge of quantum information.The second chapter introduces the basic knowledge of quantum open systems,the concept of Markov environment and non-Markov environment and the difference between the two.It also introduces the main method adopted in this paper-non-Markov quantum state diffusion(QSD)method.,theoretical derivation and some of its advantages.The third chapter introduces the concept,development history and basic principles of quantum dense coding.The fourth chapter discusses the effect of the non-Markov effect on the quantum dense coding in the Heisenberg XXZ model.The influence of the external magnetic field B and DM interaction on the quantum dense coding in the two-bit Heisenberg XXZ spin chain model is also studied.The relationship between the channel capacity of the quantum dense coding and other parameters is calculated by the definition of the densely encoded channel capacity.Comparing the initial state,the ambient noise correlation coefficient,the coupling constant of the XY plane,and the coupling constant of the z direction to the optimal dense coded channel capacity,it is found that the reduction of the parameters in different initial states can effectively improve the quantum denseness.The coding channel capacity,non-Markov memory effect plays a positive role in the quantum dense coding channel capacity;When the initial state (?),increasingJ_x _yhas a negative effect on the dense coded channel capacity,andJ_z has a positive effect on the dense coded channel capacity;For the initial statey(?),J_x _yplays a positive role in the dense coded channel capacity,whereasJ_z plays a negative role.In addition,under the influence of the ambient noise correlation coefficientgwhen the quantum channel is in the isolated state,the system dense coded channel capacity gradually increases with time,and will tend to be greater than 1 stable value under the long-term limit,which is still superior to the channel capacity of classical communication.The effects of quantum dense coding in the applied magnetic field DM and the interactive two-bit Heisenberg XXZ model are also studied later.The results show that when the uniform magnetic fieldB_z is greater than zero,the uniform magnetic fieldB_z has an obvious effect on the enhancement of the quantum dense coded channel capacity.The DM interaction plays a positive role in the quantum densely encoded channel capacity.These results show that by appropriately combining these controllable parameters,the channel capacity of quantum dense coding can be improved,thereby achieving optimal quantum dense coding.