Solid-state spin defects, especially nuclear spins with potentially achievable long coherence times, are compelling candidates for quantum memories and sensors. However, their current performances are still limited by the decoherence due to the variation of their intrinsic quadrupole and hyperfine interactions. We propose an \textit{unbalanced echo} to overcome this challenge by using a second spin to refocus the variation of these interactions, which preserves the quantum information stored in the free evolution. The unbalanced echo can be used to probe the temperature and strain distribution in materials. Experimentally, we demonstrate a 20-fold T2∗ coherence time increase in an ensemble of ∼1010 nuclear spins in diamond. Theoretically, we develop first-principles methods to predict these interaction variations and reveal their correlation in large temperature and strain ranges. We numerically show that our method can refocus stronger noise variations than our current experiments and achieves a 400-fold coherence improvement for a 25~K temperature inhomogeneity.
@article{arxiv.2205.02790,
title = {Characterizing temperature and strain variations with qubit ensembles for their robust coherence protection},
author = {Guoqing Wang and Ariel Rebekah Barr and Hao Tang and Mo Chen and Changhao Li and Haowei Xu and Ju Li and Paola Cappellaro},
journal= {arXiv preprint arXiv:2205.02790},
year = {2023}
}