Coherent storage of quantum information is crucial to many quantum technologies. Long coherence times have been demonstrated in trapped-ion qubits, typically using the hyperfine levels within the ground state of a single ion. However, recent research suggests qubits encoded in metastable states could provide architectural benefits for quantum information processing, such as the possibility of effective dual-species operation in a single-species system and erasure-error conversion for fault-tolerant quantum computing. Here we demonstrate long-lived encoding of a quantum state in the metastable states of a trapped ion. By sympathetically cooling with another ion of the same species and constantly monitoring for erasure errors, we demonstrate a coherence time of 136(42) seconds with a qubit encoded in the metastable 5D5/2 state of a single 137Ba+ ion. In agreement with a model based on empirical results from dynamical-decoupling-based noise spectroscopy, we find that dephasing of the metastable levels is the dominant source of error once erasure errors are removed.
@article{arxiv.2408.00975,
title = {Long-lived metastable-qubit memory},
author = {Xiaoyang Shi and Jasmine Sinanan-Singh and Kyle DeBry and Susanna L. Todaro and Isaac L. Chuang and John Chiaverini},
journal= {arXiv preprint arXiv:2408.00975},
year = {2024}
}