超导量子计算：长退相干量子比特发展之路  

The road to long coherence time superconducting quantum bits

作　　者：金贻荣[1] 郑东宁[1] 

机构地区：[1]中国科学院物理研究所,凝聚态国家实验室,超导国家重点实验室,北京100190

出　　处：《科学通报》2017年第34期3935-3946,共12页Chinese Science Bulletin

基　　金：国家重点基础研究发展计划(2014CB921401);国家自然科学基金(11374344,11674376)资助

摘　　要：超导量子计算是基于约瑟夫森结电路的固态量子计算技术方案.由于其易于扩展、耦合与操控等特点,已成为最有可能实现实用量子计算机/模拟机的候选方案之一.由于固态器件复杂的电磁环境,超导量子比特一直受到退相干时间不足的制约.本文简要介绍了超导量子比特的基本结构并重点论述了近期发展出的几种新型长退相干时间超导量子比特,包括Transmon/Xmon,Fluxonium和C-shunt Flux qubit等,整理了这几个不同设计方案在抑制电荷、磁通和准粒子等几种主要噪声来源方面做出的探索和贡献.最后,对几种主要的设计思想做了简要的归纳总结,以期对未来进一步发展提供参考和依据.Superconducting quantum computing is a solid state quantum computing technology based on Josephson junction circuits. It becomes one of the most promising candidates for realizing practical quantum computer/simulator, because of its scalability, easy to coupling and control, compatibility to semiconductor technologies, etc. As the complicated electromagnetic environment in solid state metal and insulator, superconducting quantum bits（qubits） suffered from shot coherence time since its early development. In this review, we described some recently developed superconducting qubit structures, including Transmon/Xmon, Fluxonium and C-shunt flux qubit. Although these new qubit structures have very different circuit parameters and energy scales, they all find their way to effectively suppress environmental noises. As a result, their coherence time were improved significantly. Transmon, a transmission-line shunted plasma oscillation qubit, was now among the most popular structures for building a multi-qubit superconducting quantum circuit. It introduced a relatively large shunt capacitor to remarkably reduce the charge dispersion. Although the non-linearity is also decreased, by operating in a properly chosen EJ/Ec, transmon can greatly reduce the charge noise while only sacrificing a small amount of non-linearity. Xmon can be considered as a modified version of transmon. It is designed and optimized for multi-qubit operation and measurement with separate X/Y and Z control lines for each qubit, and a readout bus（a transmission line or a low-Q bandpass filter） for simultaneous readout of all the qubits. Fluxonium provide another solution for suppressing the charge noise in Cooper-pair box（CPB）. It introduces a large shunt inductance to filter low-frequency offset charge in the small capacitor of the phase-slip junction（the small junction）. To keep the qubit operating in the charge region, the shunt inductor should be large enough to keep the impedance larger than the superconducting impedance quantum RQ-1

关 键 词：量子计算 超导量子比特 退相干时间 约瑟夫森结 

分 类 号：O413[理学—理论物理]