1Hefei National Laboratory for Physical Sciences at the Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China 2Shanghai Branch, CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai 201315, China 3Shanghai Research Center for Quantum Sciences, Shanghai 201315, China 4Henan Key Laboratory of Quantum Information and Cryptography, Zhengzhou 450000, China
Abstract：High-fidelity two-qubit gates are essential for the realization of large-scale quantum computation and simulation. Tunable coupler design is used to reduce the problem of parasitic coupling and frequency crowding in many-qubit systems and thus thought to be advantageous. Here we design an extensible 5-qubit system in which center transmon qubit can couple to every four near-neighboring qubits via a capacitive tunable coupler and experimentally demonstrate high-fidelity controlled-phase (CZ) gate by manipulating central qubit and one near-neighboring qubit. Speckle purity benchmarking and cross entropy benchmarking are used to assess the purity fidelity and the fidelity of the CZ gate. The average purity fidelity of the CZ gate is 99.69$\pm 0.04$% and the average fidelity of the CZ gate is 99.65$\pm 0.04$%, which means that the control error is about 0.04%. Our work is helpful for resolving many challenges in implementation of large-scale quantum systems.
Koch J, Yu T M, Gambetta J, Houck A A, Schuster D I, Majer J, Blais A, Devoret M H, Girvin S M, and Schoelkopf R J 2007 Phys. Rev. A76 042319
[8]
Barends R, Kelly J, Megrant A, Sank D, Jeffrey E, Chen Y, Yin Y, Chiaro B, Mutus J, Neill C, O'Malley P, Roushan P, Wenner J, White T C, Cleland A N, and Martinis J M 2013 Phys. Rev. Lett.111 080502
Chen Y, Neill C, Roushan P, Leung N, Fang M, Barends R, Kelly J, Campbell B, Chen Z, Chiaro B, Dunsworth A, Jeffrey E, Megrant A, Mutus J Y, O'Malley P J J, Quintana C M, Sank D, Vainsencher A, Wenner J, White T C, Geller M R, Cleland A N, and Martinis J M 2014 Phys. Rev. Lett.113 220502
[11]
Yan F, Krantz P, Sung Y, Kjaergaard M, Campbell D L, Orlando T P, Gustavsson S, and Oliver W D 2018 Phys. Rev. Appl.10 054062
[12]
Niskanen A O, Harrabi K, Yoshihara F, Nakamura Y, Lloyd S, and Tsai J S 2007 Science316 723
[13]
Hime T, Reichardt P A, Plourde B L T, Robertson T L, Wu C E, Ustinov A V, and Clarke J 2006 Science314 1427
[14]
Li X, Cai T, Yan H, Wang Z, Pan X, Ma Y, Cai W, Han J, Hua Z, Han X, Wu Y, Zhang H, Wang H, Song Y, Duan L, and Sun L 2020 Phys. Rev. Appl.14 024070
[15]
Sung Y, Ding L, Braumüller J, Vepsäläinen A, Kannan B, Kjaergaard M, Greene A, Samach G O, McNally C, Kim D, Melville A, Niedzielski B M, Schwartz M E, Yoder J L, Orlando T P, Gustavsson S, and Oliver W D 2021 Phys. Rev. X11 021058
[16]
Foxen B, Neill C, Dunsworth A, Roushan P, Chiaro B, Megrant A, Kelly J, Chen Z, Satzinger K, Barends R, Arute F, Arya K, Babbush R, Bacon D, Bardin J C, Boixo S, Buell D, Burkett B, Chen Y, Collins R, Farhi E, Fowler A, Gidney C, Giustina M, Graff R, Harrigan M, Huang T, Isakov S V, Jeffrey E, Jiang Z, Kafri D, Kechedzhi K, Klimov P, Korotkov A, Kostritsa F, Landhuis D, Lucero E, McClean J, McEwen M, Mi X, Mohseni M, Mutus J Y, Naaman O, Neeley M, Niu M, Petukhov A, Quintana C, Rubin N, Sank D, Smelyanskiy V, Vainsencher A, White T C, Yao Z, Yeh P, Zalcman A, Neven H, and Martinis J M (Google AI Quantum) 2020 Phys. Rev. Lett.125 120504
[17]
Collodo M C, Herrmann J, Lacroix N, Andersen C K, Remm A, Lazar S, Besse J C, Walter T, Wallraff A, and Eichler C 2020 Phys. Rev. Lett.125 240502
[18]
Xu H, Li W L Z, Han J, Zhang J, Linghu K, Chen Y L M, Yang Z, Wang J, Ma T, Xue G, Jin Y, and Yu H 2021 Chin. Phys. B30 044212
[19]
Barends R, Quintana C M, Petukhov A G, Chen Y, Kafri D, Kechedzhi K, Collins R, Naaman O, Boixo S, Arute F, Arya K, Buell D, Burkett B, Chen Z, Chiaro B, Dunsworth A, Foxen B, Fowler A, Gidney C, Giustina M, Graff R, Huang T, Jeffrey E, Kelly J, Klimov P V, Kostritsa F, Landhuis D, Lucero E, McEwen M, Megrant A, Mi X, Mutus J, Neeley M, Neill C, Ostby E, Roushan P, Sank D, Satzinger K J, Vainsencher A, White T, Yao J, Yeh P, Zalcman A, Neven H, Smelyanskiy V N, and Martinis J M 2019 Phys. Rev. Lett.123 210501
[20]
Boixo S, Isakov S V, Smelyanskiy V N, Babbush R, Ding N, Jiang Z, Bremner M J, Martinis J M, and Neven H 2018 Nat. Phys.14 595
[21]
Arute F, Arya K, Babbush R, Bacon D, Bardin J, Barends R, Biswas R, Boixo S, Brandao F, Buell D, Burkett B, Chen Y, Chen Z, Chiaro B, Collins R, Courtney W, Dunsworth A, Farhi E, Foxen B, and Martinis J 2019 Nature574 505
[22]
Mutus J Y, White T C, Barends R, Chen Y, Chen Z, Chiaro B, Dunsworth A, Jeffrey E, Kelly J, Megrant A, Neill C, O'Malley P J J, Roushan P, Sank D, Vainsencher A, Wenner J, Sundqvist K M, Cleland A N, and Martinis J M 2014 Appl. Phys. Lett.104 263513
Yan Z, Zhang Y R, Gong M, Wu Y, Zheng Y, Li S, Wang C, Liang F, Lin J, Xu Y, Guo C, Sun L, Peng C Z, Xia K, Deng H, Rong H, You J Q, Nori F, Fan H, Zhu X, and Pan J W 2019 Science364 753
2021, Vol. 38 
