多种热库环境对超导量子比特量子关联影响的研究

发布时间：2018-04-04 09:40

本文选题：量子比特　切入点：退相干　出处：《江西师范大学》2012年硕士论文

【摘要】：随着量子计算和量子通信技术的发展，超导量子比特在量子信息技术中已显示出了巨大的潜能。固态量子比特更是因为它的可集成性而成为实现量子计算机最具有潜力的元件之一。但由于环境对量子比特的耗散作用过强，在量子调控过程中，量子比特与环境的相互作用或者其他的原因，会导致量子相干性的消失，从而使量子信息散失在无法控制的环境中，出现退相干现象。量子关联被认为是研究量子信息过程中必不可少的一种资源，为此，我们研究了初始纠缠的量子比特在不同的环境下纠缠度和量子失协的动力学演化。 1.基于电路理论与Bloch-Redfield方程，研究了超导磁通量子比特电路的动力学演化。在二能级近似下，我们比较分析了欧姆、亚欧姆、以及超欧姆热库环境对超导磁通量子比特退相干的影响。研究结果表明：(1)一般来说可以通过选取弱耦合系数，尽量降低与环境的耦合，获得相对长的退相干时间；(2)相比较来说,在其他条件不变时，构建一个亚欧姆热库环境或超欧姆热库环境更有利于提高退相干时间；(3)超欧姆热库环境下，提高环境指标系数有利于延长超导磁通量子比特的退相干时间。因此，在一定的条件下，我们可以通过优化电路的设计，利用电感线圈间的耦合效应，降低系统的退相干。 2．我们在不同环境耗散模型下，给出了耦合量子比特量子关联的动力学演化，比较研究了共生纠缠度和量子失协的变化特点。研究发现纠缠度强烈地依赖于初始环境，并在演化过程中不可避免地发生纠缠死亡(ESD)现象；在一定的初始条件下，纠缠的演化会出现坍塌和复苏效应(dark and bright periods)，，但最终纠缠度仍会等于零。由于退相干的影响，尽管量子失协也会最终减小到零，但与纠缠的演化不同，量子失协一般不会发生纠缠突然死亡现象，而且量子失协生存时间更长，也就是说利用量子失协更有利于量子信息处理。
[Abstract]:With the development of quantum computing and quantum communication technology, superconducting quantum bits have shown great potential in quantum information technology.Solid-state quantum bits have become one of the most promising components for quantum computers because of their integrability.However, due to the excessive dissipation of the environment to the quantum bits, the interaction between the quantum bits and the environment or other reasons will lead to the disappearance of quantum coherence in the process of quantum regulation.Thus, quantum information is lost in an uncontrollable environment and decoherence occurs.Quantum correlation is considered to be an essential resource in the study of quantum information. Therefore, we study the degree of entanglement and the dynamical evolution of quantum disconnection in different environments.1.Based on circuit theory and Bloch-Redfield equation, the dynamical evolution of superconducting magnetic flux subbit circuits is studied.In the two-level approximation, we compare and analyze the effects of ohmic, sub-ohmic, and ultra-ohmic heat pool environments on superconducting magnetic flux bit decoherence.The results show that in general, the weak coupling coefficient can be selected to minimize the coupling with the environment and obtain a relatively long time of decoherence.The construction of a sub-ohm heat reservoir environment or a super-ohmic heat reservoir environment is more conducive to increasing the decoherence time and increasing the environmental index coefficient to prolong the decoherence time of superconducting magnetic fluxons.Therefore, under certain conditions, we can reduce the system decoherence by optimizing the circuit design and utilizing the coupling effect between inductance coils.2.Under different environment dissipation models, we give the dynamics evolution of quantum correlation of coupled quantum bits, and compare the characteristics of the degree of symbiotic entanglement and quantum disconnection.It is found that the degree of entanglement is strongly dependent on the initial environment, and the phenomenon of entanglement death (ESDs) inevitably occurs in the evolution process, and under certain initial conditions,The evolution of entanglement will result in collapse and resuscitation effect, but the degree of entanglement will be equal to zero in the end.Because of the effect of decoherence, quantum disassociation will eventually be reduced to zero, but unlike the evolution of entanglement, quantum decoupling usually does not occur entanglement sudden death phenomenon, and quantum disassociation survival time is longer.That is to say, it is more advantageous to process quantum information by using quantum disconnection.
【学位授予单位】：江西师范大学
【学位级别】：硕士
【学位授予年份】：2012
【分类号】：O413.1;TP38

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