Jinming Guo

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

  1. Weiping Yuan,
  2. Silu Zhao,
  3. Li Li,
  4. Chenglin Deng,
  5. Zhenghe Liu,
  6. Yu Liu,
  7. Tianming Li,
  8. Mingchuan Wang,
  9. Bingjie Chen,
  10. Guihan Liang,
  11. Jiacheng Song,
  12. Jinming Guo,
  13. Shuaili Wang,
  14. Mingxuan Zhou,
  15. Xiaohui Song,
  16. Kai Xu,
  17. Heng Fan,
  18. Zhongcheng Xiang,
  19. and Dongning Zheng
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.
arxiv pdf

Demonstration of High-Fidelity Gates in a Strongly Anharmonic with Long-Coherence C-Shunt Flux Qubit

  1. Silu Zhao,
  2. Li Li,
  3. Weiping Yuan,
  4. Xinhui Ruan,
  5. Jinzhe Wang,
  6. Bingjie Chen,
  7. Yunhao Shi,
  8. Guihan Liang,
  9. Shi Xiao,
  10. Jiacheng Song,
  11. Jinming Guo,
  12. Xiaohui Song,
  13. Kai Xu,
  14. Heng Fan,
  15. Zhongcheng Xiang,
  16. and Dongning Zheng
We demonstrate high-fidelity single-qubit gates on a C-shunt flux qubit that simultaneously combines a large anharmonicity (/2π=848 MHz) with long relaxation time (T1=23 μs). The
large anharmonicity significantly suppresses leakage to higher energy levels, enabling fast and precise microwave control. Using DRAG pulses and randomized benchmarking, the qubit achieves gate fidelities exceeding 99.9\%, highlighting the capability of C-shunt flux qubits for robust and high-performance quantum operations. These results establish them as a promising platform for scalable quantum information processing.
arxiv pdf