Curator's Take
This article demonstrates that a nickel‑vacancy center in diamond can serve as an optically addressable spin qubit with millisecond‑scale coherence at just 1.65 K, showing that transition‑metal defects can overcome the long‑standing trade‑off between optical efficiency and memory time that has limited NV and SiV platforms. By achieving all‑optical Raman control and extending $T_2$ from a few hundred nanoseconds to over a millisecond with dynamical decoupling, the work provides a practical route to compact, closed‑cycle cryogenic quantum nodes that emit in the near‑infrared telecom window. The result positions NiV⁻ as a promising building block for scalable quantum networks where long‑lived memory and high‑fidelity photon interfacing can be realized without bulky microwave hardware.
— Mark Eatherly
Summary
Quantum networks require qubits that combine efficient optical access, coherent control, and long-lived quantum memory, but realizing all three in one scalable platform remains a central bottleneck. Diamond color centers are leading candidates, yet widely studied defects retain tradeoffs among these capabilities. Here, we show that transition-metal defects in diamond provide a distinct route beyond these platforms by combining spin-orbit protected ground-state coherence, all-optical control, and near-infrared emission. Using a single nickel-vacancy (NiV$^-$), we demonstrate an all-optically controlled diamond spin qubit with coherence exceeding one millisecond at 1.65 K, compatible with compact closed-cycle cryogenics. We implement Raman Rabi oscillations and Ramsey interferometry and use all-optical dynamical decoupling to extend coherence from $T_2^*$ = 371 ns to $T_2^{CPMG-4}$ = 1.27 ms, establishing NiV$^-$ as a deployable diamond spin-photon interface.