【作者】 赵寿宽；

【导师】 赵士平；

【作者基本信息】 中国科学院大学(中国科学院物理研究所) ， 凝聚态物理学， 2021， 博士

【摘要】 量子计算是基于量子力学基本原理和量子算法的一种新型计算方式,至少在某些特定的方面将会超越经典计算而带来计算能力上的根本提高,其依托的量子系统同时也是一个很好的量子物理模拟平台。超导电路具有能耗低、易扩展、易操控和相对较长的量子相干时间等特点,在实现量子计算和量子模拟方面是最具优势的方案之一。本文的研究工作主要围绕如何利用超导电路实现量子模拟实验平台,并以此通过纵场驱动方法进行量子多体系统的非平衡动力学问题研究。所取得的主要成果包括:(1)基于电路量子电动力学的基本原理,并考虑各种量子比特的结构及等效电路,用Ledit绘图软件成功设计了一维链状超导10量子比特器件,其中利用HFSS,Maxwell等电磁仿真软件对设计模板的耦合电容、耦合电感、谐振腔特性等进行了细致的仿真。(2)系统学习了超导量子比特的微纳加工工艺,参与了铝膜与铌膜为基底的超导10量子比特以及约瑟夫森参量放大器的制备。过程中摸索出铝膜湿法刻蚀工艺,该工艺参数稳定,刻蚀效果良好,测量表明制备的铝膜与铌膜为基底的10比特器件均特性良好。(3)搭建了一套超导多量子比特测量系统,从制冷机的内部布线,衰减器和滤波器的选择,到放大器的安装调试和室温外差混频方案的布置。基于对外差解模原理的研究,提出并成功使用了一种基于希尔伯特变换的单通道外差解模方案。(4)利用搭建的测量系统完成了超导10量子比特器件的标定和测量参数的优化,包括单、两量子比特门的优化和纠缠态的制备,以及得到周期场驱动下有效耦合强度的Bessel函数形式。(5)通过周期场驱动对系统哈密顿量的调制,研究了 XY模型在可调耦合强度下的量子行走和单粒子动力学行为,实现了动力学局域化和SSH模型,观察到拓扑边缘态的存在。(6)通过周期场驱动实现了系统有效哈密顿量的反号,从而实现了时间反演操作。在此基础上研究了 Bell初态下的Loschmidt回波现象,讨论了这一重要现象在超导量子比特系统中的特殊行为。(7)通过时间反演进一步测量了系统的非时序关联(OTOC),以此研究了Néel初态下多体系统中的量子算符和量子信息的传播行为,并讨论了近可积系统中的非平衡动力学性质。更多还原

【Abstract】 Quantum computing is based on the principles of quantum mechanics and quantum algorithm,which is expected to outperform universal classical computing in certain aspects.The physical systems for quantum computing are also an excellent platform for quantum simulation studies.Superconducting circuits are among the most promising candidates for quantum computing and quantum simulation due to their advantages of low dissipation,scalability,flexibility,and relatively long coherence time.This Ph.D.thesis work involved and utilized the superconducting circuits for the experimental studies of nonequilibrium dynamics in quantum many-body systems.The main results and achievements include:(1)Based on the principles of circuit quantum electrodynamics and considering the qubit structures and equivalent circuits in various forms,one-dimensional superconducting 10-qubit array devices were designed using Ledit software.The coupling capacitance and inductance as well as the resonant cavity characteristics in the circuits were carefully simulated using HFSS,Maxwell,and other electromagnetic simulation software.(2)Using the standard micro-nano fabrication techniques,the superconducting 10qubit devices and Josephson parametric amplifiers with A1 and Nb base layers were prepared.The aluminum film wet etching process was explored with good sample stability and reproducibility.Satisfactory performance of the devices was demonstrated.(3)A multiqubit measurement system,including the internal wirings in the refrigerator,attenuators and filters,various amplifiers,and room-temperature heterodyne mixing,was successfully built.A single-channel heterodyne demodulation scheme based on Hilbert transform was proposed and used in this work.(4)Based on the multiqubit measurement system,the superconducting 10-qubit device was fully characterized.The detailed optimizations of various pulse signals and measurement parameters were performed.High fidelities of single-and two-qubit gates,and entangled Bell states were achieved.(5)The periodic longitudinal-field driving was used to tune the effective coupling strength between qubits,demonstrating a fair Bessel-function-form dependence against the driving amplitude.In this way,quantum walk and dynamic behavior in the XY model describing the 10-qubit system with tunable coupling were investigated.Dynamic localization and edge state in the realized SSH model were observed.(6)The periodic driving was further used to change the sign of the effective Hamiltonian and realize the time reversal of quantum evolution.Taking advantage of this timereversal process,the Loschmidt echo experiment with a Bell initial state was performed and its special property arising from the superconducting multiqubit Hamiltonian was discussed.(7)Finally,the out-of-time-order correlators(OTOCs)with the Neel initial state were successfully measured.A light-cone-like operator propagation was clearly observed.The results were discussed and explained in terms of nonequilibrium processes in the near integrable quantum system.更多还原