Zhao Peng, Xu Peng, Lan Dong, Chu Ji, Tan Xinsheng, Yu Haifeng, Yu Yang
National Laboratory of Solid State Microstructures, School of Physics, Nanjing University, Nanjing 230039, China.
Institute of Quantum Information and Technology, Nanjing University of Posts and Telecommunications, Nanjing 210003, China.
Phys Rev Lett. 2020 Nov 13;125(20):200503. doi: 10.1103/PhysRevLett.125.200503.
For building a scalable quantum processor with superconducting qubits, ZZ interaction is of great concern because its residual has a crucial impact to two-qubit gate fidelity. Two-qubit gates with fidelity meeting the criterion of fault-tolerant quantum computation have been demonstrated using ZZ interaction. However, as the performance of quantum processors improves, the residual static ZZ can become a performance-limiting factor for quantum gate operation and quantum error correction. Here, we introduce a superconducting architecture using qubits with opposite-sign anharmonicity, a transmon qubit, and a C-shunt flux qubit, to address this issue. We theoretically demonstrate that by coupling the two types of qubits, the high-contrast ZZ interaction can be realized. Thus, we can control the interaction with a high on-off ratio to implement two-qubit controlled-Z gates, or suppress it during two-qubit gate operation using XY interaction (e.g., an iSWAP gate). The proposed architecture can also be scaled up to multiqubit cases. In a fixed coupled system, ZZ crosstalk related to neighboring spectator qubits could also be heavily suppressed.
为了构建具有超导量子比特的可扩展量子处理器，ZZ相互作用备受关注，因为其残余对双量子比特门保真度有至关重要的影响。已经证明使用ZZ相互作用的双量子比特门的保真度符合容错量子计算的标准。然而，随着量子处理器性能的提高，残余的静态ZZ可能成为量子门操作和量子纠错的性能限制因素。在此，我们引入一种超导架构，使用具有相反符号非谐性的量子比特、一个跨导量子比特和一个C型并联磁通量子比特来解决这个问题。我们从理论上证明，通过耦合这两种类型的量子比特，可以实现高对比度的ZZ相互作用。因此，我们可以以高开关比控制这种相互作用，以实现双量子比特受控Z门，或者在使用XY相互作用（例如iSWAP门）的双量子比特门操作期间抑制它。所提出的架构也可以扩展到多量子比特情况。在一个固定的耦合系统中，与相邻旁观者量子比特相关的ZZ串扰也可以被大幅抑制。
