Introducing Anharmonicity into Coupler for Suppressing ZZ Coupling: Toward Large‐Scale Scalable Superconducting Quantum Chip

ABSTRACT The intrinsic parasitic longitudinal (ZZ) coupling between coupled qubits degrades the fidelity of quantum gate operations, becoming a major limiting factor for building large‐scale, scalable superconducting quantum chips. Therefore, it is essential to develop a coupling scheme that can flexibly control the ZZ interaction. This work proposes a simple coupling architecture that enables high‐fidelity quantum gate operations via tunable ZZ coupling. The scheme leverages a bus resonator with anharmonicity to effectively suppress the ZZ coupling between two frequency‐tunable Xmon qubits. Moreover, theoretical demonstrations show that the ZZ interaction can be tuned via qubit frequency adjustment, thus enabling two‐qubit controlled‐Z (CZ) gates. Finally, the fidelity of gate operations is evaluated using cross‐entropy benchmarking, realizing a CZ gate fidelity of (99.310.04)%. This work demonstrates flexible ZZ coupling control without increasing circuit complexity, offering a new paradigm for the development of large‐scale superconducting quantum processors with simplified control wiring.