Randomized Benchmarking of a Remote cnot Gate Via a Meter-Scale Microwave Link

High-fidelity, meter-scale microwave interconnects between superconducting quantum processor modules are a key technology for extending the system size beyond constraints imposed by device manufacturing equipment, yield, and signal delivery. Although tomographic experiments have been used in previous demonstrations for benchmarking remote state transfer between modules, they do not reliably separate state preparation and measurement (SPAM) error from the error per state transfer. Recent developments based on randomized benchmarking provide a compatible theory for separating these two errors. In this Letter, we present a module-to-module interconnect based on tunable-coupling qubits and benchmark, in a SPAM-error-tolerant manner enabled by a frame-tracking technique, a remote state transfer fidelity of 98.8% across a 60 cm-long coplanar waveguide (CPW). The state transfer is implemented via a superadiabatic transitionless driving method, which suppresses intermediate excitation in the internal modes of the CPW. We further propose and construct a remote cnot gate between modules, composed of local controlled-Z (CZ) gates in each module and remote state transfers, and report a gate fidelity of 93.3% using the randomized benchmarking method. The remote cnot construction and benchmarking we present provide a way to fully characterize the module-to-module link operation and standardize reporting fidelity, analogous to randomized benchmarking protocols for other quantum gates.