Restless Tuneup of High-Fidelity Qubit Gates

TL;DR

This paper introduces a rapid tuneup protocol for high-fidelity qubit gates that significantly accelerates the calibration process by using real-time measurements and a novel cost function, achieving near-perfect fidelity in one minute.

Contribution

The authors develop a fast, measurement-based tuneup protocol for qubit gates that reduces calibration time tenfold compared to traditional methods, with potential extension to two-qubit gates.

Findings

Achieved 0.999 average Clifford fidelity in one minute

Demonstrated nearly constant signal-to-noise ratio for detecting fractional error changes

Protocol applicable to both single and two-qubit gate tuneup

Abstract

We present a tuneup protocol for qubit gates with tenfold speedup over traditional methods reliant on qubit initialization by energy relaxation. This speedup is achieved by constructing a cost function for Nelder-Mead optimization from real-time correlation of non-demolition measurements interleaving gate operations without pause. Applying the protocol on a transmon qubit achieves 0.999 average Clifford fidelity in one minute, as independently verified using randomized benchmarking and gate set tomography. The adjustable sensitivity of the cost function allows detecting fractional changes in gate error with nearly constant signal-to-noise ratio. The restless concept demonstrated can be readily extended to the tuneup of two-qubit gates and measurement operations.