Three-Qubit Randomized Benchmarking

TLDR

Scalable multiqubit fidelity metrics are essential as quantum circuits grow in size. The authors aim to perform the first three‑qubit randomized benchmarking on a device of three fixed‑frequency transmon qubits. They benchmark the device using pairwise microwave‑activated cross‑resonance interactions among the qubits. The three‑qubit error per Clifford was measured as 0.106 for all‑to‑all connectivity and 0.207 for linear connectivity; the errors can be predicted from one‑ and two‑qubit RB, but coherent errors can raise the error to 0.302 beyond that prediction, underscoring the need for multiqubit metrics.

Abstract

As quantum circuits increase in size, it is critical to establish scalable multiqubit fidelity metrics. Here we investigate, for the first time, three-qubit randomized benchmarking (RB) on a quantum device consisting of three fixed-frequency transmon qubits with pairwise microwave-activated interactions (cross-resonance). We measure a three-qubit error per Clifford of 0.106 for all-to-all gate connectivity and 0.207 for linear gate connectivity. Furthermore, by introducing mixed dimensionality simultaneous RB---simultaneous one- and two-qubit RB---we show that the three-qubit errors can be predicted from the one- and two-qubit errors. However, by introducing certain coherent errors to the gates, we can increase the three-qubit error to 0.302, an increase that is not predicted by a proportionate increase in the one- and two-qubit errors from simultaneous RB. This demonstrates the importance of multiqubit metrics, such as three-qubit RB, on evaluating overall device performance.