Randomized benchmarking of a high-fidelity remote CNOT gate over a meter-scale microwave interconnect

TL;DR

This paper demonstrates high-fidelity remote quantum state transfer and a CNOT gate between superconducting modules over a meter-scale microwave interconnect, using randomized benchmarking to accurately assess performance.

Contribution

It introduces a novel remote CNOT gate and benchmarking method for module-to-module links, improving fidelity measurement accuracy in superconducting quantum systems.

Findings

Remote state transfer fidelity of 0.988 over 60cm

Remote CNOT gate fidelity of 0.933

SPAM-error-tolerant benchmarking technique

Abstract

High-fidelity, meter-scale microwave interconnects between superconducting quantum processor modules are a key technology for extending 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 work, we present a module-to-module interconnect based on Tunable-Coupling Qubits (TCQs) and benchmark, in a SPAM-error-tolerant manner enabled by a frame-tracking technique, a remote state transfer fidelity of 0.988 across a 60cm-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 CZ gates in each module and remote state transfers, and report a gate fidelity of 0.933 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.