Simultaneous Feedback and Feedforward Control and Its Application to Realize a Random Walk on the Bloch Sphere in an Xmon-Superconducting-Qubit System

Liang Xiang, Zhiwen Zong, Zhenhai Sun, Ze Zhan, Ying Fei, Zhangjingzi Dong, Chongxin Run, Zhilong Jia, Peng Duan, Jianlan Wu, Yi Yin, and Guoping Guo

Phys. Rev. Applied 14, 014099 – Published 31 July 2020

Abstract

Measurement-based feedback control is central in quantum computing and precise quantum control. Here we realize a fast and flexible field-programmable-gate-array-based feedback control in an Xmon- superconducting-qubit system. The latency of room-temperature electronics is custom-optimized to be as short as 140 ns. Projective measurement of a signal qubit produces a feedback tag to implement a conditional pulse gate on the qubit. In a feedforward process, the measurement-based feedback tag is brought to a different target qubit for conditional control. In a two-qubit experiment, the feedback and feedforward controls are simultaneously implemented in consecutive steps. A quantum number is then generated by the signal qubit, and a random walk of the target qubit is correspondingly triggered and realized on the Bloch sphere. Our experiment provides a conceptually simple and intuitive benchmark for feedback control in a multiqubit system. The feedback system can be further scaled up for more-complex feedback-control experiments.

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Received 21 September 2019
Revised 3 May 2020
Accepted 18 June 2020

DOI:https://doi.org/10.1103/PhysRevApplied.14.014099

Physics Subject Headings (PhySH)

Continuous-time random walk Quantum computation Quantum control Quantum feedback Quantum information with solid state qubits Quantum tomography

Superconducting qubits

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Liang Xiang¹, Zhiwen Zong¹, Zhenhai Sun¹, Ze Zhan¹, Ying Fei¹, Zhangjingzi Dong¹, Chongxin Run¹, Zhilong Jia², Peng Duan², Jianlan Wu^1,†, Yi Yin ^1,*, and Guoping Guo^2,3,‡

¹Zhejiang Province Key Laboratory of Quantum Technology and Device, Department of Physics, Zhejiang University, Hangzhou 310027, China
²Key Laboratory of Quantum Information, University of Science and Technology of China, Hefei 230026, China
³Origin Quantum Computing, Hefei 230026, China

^*yiyin@zju.edu.cn
^†jianlanwu@zju.edu.cn
^‡gpguo@ustc.edu.cn

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Vol. 14, Iss. 1 — July 2020

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