Characterizing errors on qubit operations via iterative randomized benchmarking

TL;DR

This paper introduces a method to differentiate between unitary and non-unitary errors in quantum gates using iterative randomized benchmarking, achieving high fidelity in superconducting qubits and identifying decoherence sources.

Contribution

The authors develop an iterative randomized benchmarking protocol that distinguishes between coherent and incoherent errors in quantum gates, improving error characterization accuracy.

Findings

Achieved 99.95% single-qubit gate fidelity.

Quadratic decay indicates unitary errors, linear decay indicates non-unitary errors.

Gate fidelity limited by decoherence, not unitary errors.

Abstract

With improved gate calibrations reducing unitary errors, we achieve a benchmarked single-qubit gate fidelity of 99.95% with superconducting qubits in a circuit quantum electrodynamics system. We present a method for distinguishing between unitary and non-unitary errors in quantum gates by interleaving repetitions of a target gate within a randomized benchmarking sequence. The benchmarking fidelity decays quadratically with the number of interleaved gates for unitary errors but linearly for non-unitary, allowing us to separate systematic coherent errors from decoherent effects. With this protocol we show that the fidelity of the gates is not limited by unitary errors, but by another drive-activated source of decoherence such as amplitude fluctuations.