超导量子比特的纠缠及宏观共振隧穿研究

发布时间：2018-01-04 15:29

本文关键词：超导量子比特的纠缠及宏观共振隧穿研究　出处：《南京大学》2017年博士论文　论文类型：学位论文

【摘要】：超导量子比特不仅对研究物理学很重要,而且对于建立可扩展的量子信息处理同样也很重要。外场作用下的超导量子比特(quantum bit,简称qubit)会与微观二能级(Two level system,简称TLS)系统耦合,并且外场对于两体qubit-TLS系统动力学性质有重要的关联。纠缠不仅发生在微观层面,在宏观系统如超导量子比特中同样存在纠缠。最近关于外场对超导系统纠缠影响的研究非常多,如纠缠振荡、纠缠死亡以及纠缠死亡又复活等。本论文针对射频超导量子干涉器中的宏观共振隧穿现象以及超导回路的宏观量子特性进行了:共振微波驱动下的超导相位量子比特与微观二能级系统耦合动力学及耦合的纠缠,单周期正弦信号驱动下的射频超导量子干涉器的宏观共振隧穿动力学等方面的系统研究。其研究成果对我们深入理解超导量子比特的宏观量子现象以及有效的操控超导量子比特的特性均有重要意义。论文的主要研究内容及创新点包括:第一,利用两体四能级耦合模型描述共振微波驱动下的两体qubit-TLS系统的动力学,该模型呈现出了该两体系统量子动力学清晰的物理背景。利用纯态下的Schrodinger方程和混态下的Lindblad主方程分别数值模拟了共振微波驱动下的两体qubit-TLS系统的动力学性质。另外,计算了微波与微观二能级系统之间不同的耦合强度对共振微波驱动下该两体qubit-TLS系统的动力学影响,结果表明微观二能级系统与微波的耦合强度对该两体qubit-TLS系统的相干性有一定的影响。以上结论对于分析具体的实验情况,比如微波同时与超导量子比特和微观二能级系统或类似的系统都存在耦合作用时该混合系统的动力学研究提供了帮助。第二,利用实验测量结果数值计算共振微波驱动的两体qubit-TLS系统的纠缠动力学。结论表明不仅可以通过测量qubit-TLS系统其中一方来定量计算两体qubit-TLS系统的纠缠度,而且可以通过调节超导量子比特与共振微波的相互作用时间来调控两体qubit-TLS系统的纠缠度。另外,数值计算了纯态和混态情况下的两体qubit-TLS系统的纠缠度。由于量子系统的退相干效应,两体混态qubit-TLS系统纠缠度呈现振荡衰减,并且出现纠缠死亡以及纠缠死亡又复活等现象。结论表明纠缠振荡以及纠缠复活是源于qubit-TLS的相互耦合作用,而纠缠死亡源于两体qubit-TLS系统与环境的耦合。第三,利用射频超导量子干涉器(rf-SQUID),实验上观测到单周期正弦信号驱动下rf-SQUIID的宏观态之间的宏观共振隧穿现象。双势阱能级间的共振隧穿峰使得超导量子比特的布居数呈现干涉图样。考虑势阱本身以及势阱之间的退相干效应,数值模拟超导量子比特的动力学与外部正弦信号的幅值、频率以及初始相位的关联。超导量子比特的布居数与外部信号参数之间的重要关联为操控量子态提供了一种新的方法。
[Abstract]:Superconducting quantum bit is important not only to study physics, but also for the establishment of scalable quantum information processing is also very important. Superconducting qubits under the applied field (quantum bit, referred to as qubit) and micro two level (Two level system, referred to as TLS) system coupling, and an important link for the field of two body dynamics the qubit-TLS system properties. Entanglement occurs not only in the micro level, the macro system such as superconducting qubit entanglement. Recently there is also very much about the influence of external field on the entanglement of the superconducting system, such as entanglement entanglement and entanglement death oscillation, death and resurrection. This thesis focuses on the macroscopic quantum properties of RF superconducting quantum interference device in macroscopic resonant tunneling the wear phenomenon and superconducting loops are: resonance microwave driven superconducting phase qubit coupled with the micro dynamics of the two level system and coupling The system of macro entanglement, the resonant tunneling RF superconducting quantum single cycle driven by sinusoidal interference device in dynamics and so on. The research results of macroscopic quantum phenomena in our understanding of superconducting qubits and characteristics of superconducting qubits are controlled effectively is of great significance. The main research contents and innovations include first, using two four level coupled dynamics model to describe the two qubit-TLS system driven by a microwave resonance, the model shows the two quantum dynamics and clear physical background. The Lindblad master equation using Schrodinger equation of pure state and mixed state respectively by numerical simulation of the dynamical properties of two qubit-TLS system microwave resonance driven. In addition, between microwave and micro two level system with different coupling strength on the two body resonance microwave driven by Q calculation The dynamic effects of ubit-TLS system, the results show a certain influence the coherence of two level system and the coupling strength of micro microwave on the two qubit-TLS system. The above conclusions for the analysis of the specific experimental situation, such as microwave and superconducting qubits and micro two level system or similar system has provided the help of coupling dynamics the hybrid system. Second, the entanglement dynamics using numerical experimental results of calculation of resonant microwave driven two qubit-TLS system. The conclusion shows that the entanglement can not only through the measurement of qubit-TLS system in which one party to calculate two body qubit-TLS system, but also to control the entanglement of two qubit-TLS system through the interaction time regulation of superconductivity quantum bit and microwave resonance. In addition, the numerical calculation of two qubit-TLS pure state and mixed states under the situation The entanglement of quantum systems. Due to decoherence, two mixed state entanglement qubit-TLS system oscillation attenuation, and the emergence of the phenomenon of entanglement entanglement death and death and resurrection. The conclusion shows that the entanglement and entanglement oscillation resurrection is mutual coupling from qubit-TLS, coupling and the entanglement death from the two qubit-TLS system with the environment. Third, using RF superconducting quantum interference device (rf-SQUID), macroscopic resonant tunneling between macroscopic state experiments of single cycle driven by sinusoidal signal of rf-SQUIID resonant tunneling phenomena. The double well potential between the levels in the peak of superconducting qubit population showed the interference pattern. Considering the potential trap itself and potential decoherence, amplitude dynamics and external sinusoidal signal simulation of superconducting qubits, frequency and initial phase correlation. Superconducting qubit population The important correlation between the number and the parameters of the external signal provides a new way to manipulate the quantum state.

【学位授予单位】：南京大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O413;O511.3

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