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

We propose $mathrm{SQiSW}$, the matrix square root of the standard $mathrm{iSWAP}$ 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 $mathrm{iSWAP}$, 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 $mathrm{iSWAP}$ gate, its capabilities surprisingly rival and even surpass that of $mathrm{iSWAP}$ or other incumbent native two-qubit gates such as $mathrm{CNOT}$. 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 $mathrm{SQiSW}$. For the reasons above, we believe that the $mathrm{SQiSW}$ gate is worth further study and consideration as a native two-qubit gate for both fault-tolerant and noisy intermediate-scale quantum (NISQ) computation.