Scalable fast benchmarking for individual quantum gates with local twirling

With the development of controllable quantum systems,fast and practical characterization of multi-qubit gates has become essential for building high-fidelity quantum computing devices.The usual way to fulfill this requirement via randomized benchmarking demands complicated implementation of numerous multi-qubit twirling gates.How to efficiently and reliably estimate the fidelity of a quantum process remains an open problem.This work thus proposes a character-cycle benchmarking protocol and a character-average benchmarking protocol using only local twirling gates to estimate the process fidelity of an individual multi-qubit operation.Our protocols were able to characterize a large class of quantum gates including and beyond the Clifford group via the local gauge transformation,which forms a universal gate set for quantum computing.We demonstrated numerically our protocols for a non-Clifford gate—controlled-(T X)and a Clifford gate—five-qubit quantum errorcorrecting encoding circuit.The numerical results show that our protocols can efficiently and reliably characterize the gate process fidelities.Compared with the cross-entropy benchmarking,the simulation results show that the character-average benchmarking achieves three orders of magnitude improvements in terms of sampling complexity.