Spin defects in diamond are promising platforms for quantum sensing. The longest electron spin relaxation times (T1) at room temperature for solid-state defects are observed in nitrogen vacancy centers in diamond, which can reach 6.67 ms, and substitutional nitrogen ("P1 centers") in diamond, which exhibit a T1 of 2 ms. No other solid-state defect has exhibited millisecond-scale spin relaxation times at room temperature thus far. Here, we characterize the spin properties of the WAR5 defect in diamond with pulsed electron spin resonance. The observed T1 is one of the longest for solid-state spin defects: 0.97(27) ms at room temperature and 14.38(19) min at 4 K. The observed coherence time (T2) is 246(7) μs, which can be extended to 6.49(34) ms at 4 K with dynamical decoupling. Furthermore, we demonstrate optical spin polarization with a range of wavelengths from 405 nm to 500 nm and propose potential zero-phonon line candidates.
@article{arxiv.2603.07265,
title = {A defect in diamond with millisecond-scale spin relaxation time at room temperature},
author = {Sounak Mukherjee and Anran Li and Johannes Eberle and Sean Karg and Zi-Huai Zhang and Mayer M. Feldman and Yilin Chen and Mark E. Turiansky and Mengen Wang and Yogendra Limbu and Tharnier O. Puel and Yueguang Shi and Matthew L. Markham and Rajesh L. Patel and Patryk Gumann and Michael E. Flatte and Chris G. Van de Walle and Stephen A. Lyon and Nathalie P. de Leon},
journal= {arXiv preprint arXiv:2603.07265},
year = {2026}
}