Tunable Nonlocal ZZ Interaction for Remote Controlled-Z Gates Between Distributed Fixed-Frequency Qubits

  1. Benzheng Yuan,
  2. Chaojie Zhang,
  3. Haoran He,
  4. Yangyang Fei,
  5. Chuanbing Han,
  6. Shuya Wang,
  7. Huihui Sun,
  8. Qing Mu,
  9. Bo Zhao,
  10. Fudong Liu,
  11. Weilong Wang,
  12. and Zheng Shan
Fault-tolerant quantum computing requires large-scale superconducting processors, yet monolithic architectures face increasing constraints from wiring density, crosstalk, and fabrication
yield. Modular superconducting platforms offer a scalable alternative, but achieving high-fidelity entangling gates between distant modules remains a central challenge, particularly for highly coherent fixed-frequency qubits. Here, we propose a distributed hardware architecture designed to overcome this bottleneck by employing a pair of double-transmon couplers (DTCs). By synchronously controlling the two DTCs stationed at opposite ends of a macroscopic cable, our scheme strongly suppresses residual static inter-module coupling while enabling on-demand activation of a non-local cross-Kerr interaction with an on/off ratio exceeding 106. Through comprehensive system-level numerical simulations incorporating realistic hardware parameters, we demonstrate that this mechanism can realize a remote controlled-Z (CZ) gate with a fidelity over 99.99\% between fixed-frequency transmons housed in separate packages interconnected by a 25 cm coaxial cable. These results establish a highly viable, hardware-efficient route toward high-performance distributed superconducting processors.