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arXiv · 2610.18477

Experimental Realization of a C-Shunt Flux-Qubit Coupler for Controlled-Z Gates between Transmons

Weiping Yuan·Silu Zhao·Li Li·Chenglin Deng·Zhenghe Liu·Yu Liu·Tianming Li·Mingchuan Wang·Bingjie Chen·Guihan Liang·Jiacheng Song·Jinming Guo·Shuaili Wang·Mingxuan Zhou·Xiaohui Song·Kai Xu·Heng Fan·Zhongcheng Xiang·Dongning Zheng
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Abstract

Fast entangling gates and low-interaction idling require distinct operating conditions in superconducting quantum processors. We experimentally realize a transmon-C-shunt-transmon (TCT) device in which a flux-tunable, three-junction capacitively shunted flux-qubit coupler connects two transmon data qubits. The C-shunt coupler provides a flux-tunable, positively anharmonic spectrum for tailoring the interactions between the data qubits. Conditional Ramsey and swap measurements identify an idle region with near-zero residual ZZ interaction strength and suppressed transverse exchange. At this bias, simultaneous single-qubit interleaved randomized benchmarking yields X-gate fldelities above 99.7%, consistent with individual operation. A 45 ns nonadiabatic controlled-Z (CZ) gate achieves an interleaved randomized benchmarking fldelity estimate of 99.23(15)%. Numerical simulations identify coupler energy relaxation as an important limitation on CZ-gate fldelity and indicate that extending the coupler lifetime can improve gate performance. These results demonstrate the experimental feasibility of C-shunt flux-qubit couplers for combining low-interaction idling with fast entangling operations between transmon qubits.

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Weiping Yuan, Silu Zhao, Li Li, Chenglin Deng, Zhenghe Liu, Yu Liu, Tianming Li, Mingchuan Wang, Bingjie Chen, Guihan Liang, Jiacheng Song, Jinming Guo, Shuaili Wang, Mingxuan Zhou, Xiaohui Song, Kai Xu, Heng Fan, Zhongcheng Xiang, Dongning Zheng. 2026-10-13. Experimental Realization of a C-Shunt Flux-Qubit Coupler for Controlled-Z Gates between Transmons. https://arxiv.org/abs/2610.18477

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