Superconducting qubits are compelling platforms for charge-parity detection and, due to their theoretical sensitivity on the meV energy scale, hold promise for rare event searches. In this work, we realize high-fidelity mapping of charge-parity states onto qubit states using an offset-charge-tunable transmon qubit and efficiently characterize the fidelity of the charge-parity detection via randomized benchmarking. Specifically, a gate control line is applied to control offset charge, allowing us to achieve the single-qubit gate fidelity up to 99.96%. We combine a net-zero-based pulse on the gate line with a spin-echo-based sequence to realize charge-parity mapping, achieving a fidelity of 99.37%. Then, we demonstrate continuous monitoring of the charge-parity state with over 93.4% fidelity at a 4-\mu s sampling interval. Finally, an error analysis of charge-parity detection is performed, and it is found that qubit readout is currently the largest source of error. We believe this work lays the foundation for future exploration of ultra-low energy particles.
@article{arxiv.2604.02809,
title = {Characterizing charge-parity detection based on an offset-charge-tunable transmon qubit via randomized benchmarking},
author = {Yao-Yao Jiang and Tang Su and Yuxiang Liu and Yi-Ming Guo and Yidong Song and Yu-Long Li and Yanjie Zeng and Guang-Ming Xue and Wei-Jie Sun and Mei-Ling Li and Yi-Rong Jin and Junhua Wang and Xuegang Li and Hai-Feng Yu},
journal= {arXiv preprint arXiv:2604.02809},
year = {2026}
}