Experimental Realization of a C-Shunt Flux-Qubit Coupler for Controlled-Z Gates between Transmons
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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BibTeX
@misc{yuan2026experimental,
title = {{Experimental Realization of a C-Shunt Flux-Qubit Coupler for Controlled-Z Gates between Transmons}},
author = {Weiping Yuan and Silu Zhao and Li Li and Chenglin Deng and Zhenghe Liu and Yu Liu and Tianming Li and Mingchuan Wang and Bingjie Chen and Guihan Liang and Jiacheng Song and Jinming Guo and Shuaili Wang and Mingxuan Zhou and Xiaohui Song and Kai Xu and Heng Fan and Zhongcheng Xiang and Dongning Zheng},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.18477},
eprint = {2610.18477},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.18477},
}
RIS
TY - UNPB
TI - Experimental Realization of a C-Shunt Flux-Qubit Coupler for Controlled-Z Gates between Transmons
AU - Weiping Yuan
AU - Silu Zhao
AU - Li Li
AU - Chenglin Deng
AU - Zhenghe Liu
AU - Yu Liu
AU - Tianming Li
AU - Mingchuan Wang
AU - Bingjie Chen
AU - Guihan Liang
AU - Jiacheng Song
AU - Jinming Guo
AU - Shuaili Wang
AU - Mingxuan Zhou
AU - Xiaohui Song
AU - Kai Xu
AU - Heng Fan
AU - Zhongcheng Xiang
AU - Dongning Zheng
PY - 2026
DA - 2026/10/13
PB - arXiv
DO - 10.48550/arxiv.2610.18477
UR - https://arxiv.org/abs/2610.18477
AB - 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.
ER -