Protecting nuclear spin ensembles against temperature and strain variations*

Solid-state spin defects, especially nuclear spins with potentially extremely long coherence times, are compelling platforms 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 unbalanced echo sequence to overcome this challenge by using a second spin to refocus the variation of these interactions, which preserves the quantum information stored in the nuclear spin 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 ∼ 10^10 nuclear spins in a 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.