Quantum Memory in Nitrogen-Vacancy Diamonds at Millikelvin Temperatures.pdf

The realization of long-lived quantum memory is a critical milestone for scalable quantum networks and error-corrected quantum computation. While nitrogen-vacancy (NV) centers in diamond have emerged as promising candidates, their coherence times at cryogenic temperatures (typically 1–10 ms at 4 K) remain limited by phonon-induced decoherence. Here, we demonstrate that cooling NV centers to millikelvin (mK) temperatures suppresses spin-phonon interactions, enabling electronic spin coherence times (T2​) exceeding 10 seconds—a three-order-of-magnitude improvement over conventional cryogenic operation. Through a combination of dynamical decoupling, superconducting shielding, and optimized material purity, we isolate the NV spin from its primary decoherence channels, entering a regime where material defects and control fidelity become the dominant limits. These results establish NV diamonds as a viable platform for fault-tolerant quantum memory and open new pathways for hybrid quantum systems integrating spins, superconductors, and photons.