Towards ultra-high fidelity quantum operations: SQiSW gate as a native two-qubit gate*

We propose SQiSW, the matrix square root of the standard iSWAP gate, as a native two-qubit gate for superconducting quantum computing. We show numerically that it has potential for an ultra-high fidelity implementation as its gate time is half of that of iSWAP, but at the same time it possesses powerful information processing capabilities in both the compilation of arbitrary two-qubit gates and the generation of large-scale entangled W-like states. Even though it is half of an iSWAP gate, its capabilities surprisingly rival and even surpass that of iSWAP or other incumbent native two-qubit gates such as CNOT. To complete the case for its candidacy, we propose a detailed compilation, calibration and benchmarking framework. In particular, we propose a variant of randomized benchmarking called interleaved fully randomized benchmarking (iFRB) which provides a general and unified solution for benchmarking non-Clifford gates such as SQiSW. For the reasons above, we believe that the SQiSW gate is worth further study and consideration as a native two-qubit gate for both fault-tolerant and noisy intermediate-scale quantum (NISQ) computation.