Robust two-qubit gates in a linear ion crystal using a frequency-modulated driving force

TL;DR

This paper introduces a frequency-modulated driving force technique to enhance the fidelity of two-qubit gates in ion trap quantum computers, effectively reducing errors and improving robustness against frequency drifts.

Contribution

The authors develop and demonstrate a novel FM driving force method that significantly suppresses errors in two-qubit gates within ion crystals, achieving high fidelity and robustness.

Findings

Error rates below 0.01% in simulations

Achieved 98.3% two-qubit gate fidelity experimentally

Method is robust against frequency drifts of ±1 kHz

Abstract

In an ion trap quantum computer, collective motional modes are used to entangle two or more qubits in order to execute multi-qubit logical gates. Any residual entanglement between the internal and motional states of the ions results in loss of fidelity, especially when there are many spectator ions in the crystal. We propose using a frequency-modulated (FM) driving force to minimize such errors. In simulation, we obtained an optimized FM two-qubit gate that can suppress errors to less than 0.01\% and is robust against frequency drifts over $\pm$1 kHz. Experimentally, we have obtained a two-qubit gate fidelity of $98.3(4)\%$, a state-of-the-art result for two-qubit gates with 5 ions.