Trapped-ion systems are one of the leading platforms for quantum information processing, where a key challenge is to scale up system size while maintaining high-fidelity two-qubit operations. A promising approach is to build high-performance modules interconnected via strong coupling. In particular, axial motional modes provide a feasible means of coupling short ion chains. However, previous implementations of fully connected 5-ion modules based on axial modes have been limited to fidelities of 96.6−98.0%. Here, we demonstrate two-qubit quantum logic gates in a 5-ion 40Ca+ chain using axial modes, achieving fidelities exceeding 99% for adjacent pairs and over 98% for arbitrary pairs by carefully tackling dominant error sources. Our results are beneficial to the development of scalable ion-trap quantum processors, quantum simulation and quantum-enhanced metrology.
@article{arxiv.2507.00504,
title = {High-fidelity two-qubit quantum logic gates in a trapped-ion chain using axial motional modes},
author = {Xingyu Zhao and Ji Bian and Yi Li and Yue Li and Mengxiang Zhang and Yiheng Lin},
journal= {arXiv preprint arXiv:2507.00504},
year = {2026}
}