High fidelity quantum gates in long chains of barium ions

Hyperfine “clock state” qubits in the ground state manifold of trapped ions offer the longest coherence times of any physical qubit to date [1]. Due to the challenge of modulating a single laser at qubit frequencies (1-10 GHz), all of the early quantum computers at IonQ used pulsed laser systems to implement stimulated Raman transitions between qubit states [2]. These pulsed laser systems have allowed for the demonstration of two qubit quantum gates on barium ions with fidelity as high as 99.9% in the two ion context. Additionally, acousto-optical deflectors (AODs) have been used to address long chains of up to 36 fully connected trapped-ion qubits while maintaining high-fidelity operations.

[1] P. Wang, C.Y. Luan, M. Qiao, et al., Single ion qubit with estimated coherence time exceeding one hour. Nat. Commun. 12, 233 (2021).

[2] J.-S. Chen, et. al., Benchmarking a trapped-ion quantum computer with 30 qubits. Quantum 8, 1516 (2024)