Angle-robust Two-Qubit Gates in a Linear Ion Crystal

TL;DR

This paper introduces an improved pulse-design method for two-qubit gates in trapped-ion quantum computers, enhancing robustness against mode frequency drifts and improving gate fidelity.

Contribution

The authors develop a novel pulse-design technique that ensures robustness of the two-qubit rotation angle against uniform mode frequency drifts, improving gate performance.

Findings

Enhanced gate fidelity under frequency drifts

Successful experimental validation of the pulse design

Improved robustness of two-qubit gates

Abstract

In trapped-ion quantum computers, two-qubit entangling gates are generated by applying spin-dependent force which uses phonons to mediate interaction between the internal states of the ions. To maintain high-fidelity two-qubit gates under fluctuating experimental parameters, robust pulse-design methods are applied to remove the residual spin-motion entanglement in the presence of motional mode frequency drifts. Here we propose an improved pulse-design method that also guarantees the robustness of the two-qubit rotation angle against uniform mode frequency drifts by combining pulses with opposite sensitivity of the angle to mode frequency drifts. We experimentally measure the performance of the designed gates and see an improvement on both gate fidelity and gate performance under uniform mode frequency offsets.