Parametric iSWAP Gate at Zero Flux Boosts Qubits

Researchers at RIKEN and Toshiba Corporation have demonstrated a high-fidelity iSWAP gate operating at zero flux bias between superconducting qubits. The circuit uses a capacitively shunted double-transmon coupler (CSDTC) which eliminates the need for static flux biasing, a common source of error in these systems, while maintaining high performance. Achieving an average gate fidelity of 99. 92(2)% in just 112 nanoseconds, the work addresses challenges posed by large flux pulses prone to distortion and decoherence, and “boost[s] further progress in the research of superconducting quantum computers.” Unlike conventional designs requiring precise, constant magnetic fields to maintain qubit performance, this new approach operates effectively around zero flux, simplifying system calibration and potentially reducing error rates. This is achieved through the CSDTC’s ability to realize a minimal residual ZZ interaction across a broad range of flux values, a feature that allows for…