High-fidelity gates in a Josephson qubit

TL;DR

This paper presents advanced measurement techniques for superconducting qubits, achieving high-fidelity single-qubit gates of 0.98 and introducing a Ramsey interference error filter to detect very small errors near fault-tolerance thresholds.

Contribution

It introduces new experimental procedures for precise error measurement and a novel metrology tool for detecting small state occupations in superconducting qubits.

Findings

Single qubit gate fidelity of 0.98 achieved.

New error measurement method separates gate and measurement errors.

Ramsey interference error filter detects occupation probabilities as low as 10^{-4}.

Abstract

We demonstrate new experimental procedures for measuring small errors in a superconducting quantum bit (qubit). By carefully separating out gate and measurement errors, we construct a complete error budget and demonstrate single qubit gate fidelities of 0.98, limited by energy relaxation. We also introduce a new metrology tool -- a Ramsey interference error filter -- that can measure the occupation probability of the state $\ket{2}$ down to $10^{-4}$, a magnitude near the fault tolerant threshold.