Batch Optimization of Frequency-Modulated Pulses for Robust Two-qubit Gates in Ion Chains

TL;DR

This paper presents a batch optimization method to enhance the robustness of frequency-modulated two-qubit gates in ion chains, effectively handling systematic errors and improving gate fidelity in experimental quantum computing.

Contribution

It introduces a novel batch optimization approach for designing robust frequency-modulated gates, outperforming traditional methods under parameter uncertainties.

Findings

Good performance up to 12 ions in simulations

Experimental validation on a two-ion chain

Enhanced robustness against motional mode-frequency offsets

Abstract

Two-qubit gates in trapped-ion quantum computers are generated by applying spin-dependent forces that temporarily entangle the internal state of the ion with its motion. Laser pulses are carefully designed to generate a maximally entangling gate between the ions while minimizing any residual entanglement between the motion and the ion. The quality of the gates suffers when the actual experimental parameters differ from the ideal case. Here, we improve the robustness of frequency-modulated M{\o}lmer-S{\o}rensen gates to motional mode-frequency offsets by optimizing the average performance over a range of systematic errors using batch optimization. We then compare this method with frequency-modulated gates optimized for ideal parameters that include an analytic robustness condition. Numerical simulations show good performance up to 12 ions, and the method is experimentally demonstrated on a two-ion chain.