Silicon-Vacancy Spin Qubit in Diamond: A Quantum Memory Exceeding 10 ms with Single-Shot State Readout

The negatively charged silicon-vacancy (SiV⁻) color center in diamond has recently emerged as a promising system for quantum photonics. Its symmetry-protected optical transitions enable the creation of indistinguishable emitter arrays and deterministic coupling to nanophotonic devices. Despite this, the longest coherence time associated with its electronic spin achieved to date (∼250 ns) has been limited by coupling to acoustic phonons. We demonstrate coherent control and suppression of phonon-induced dephasing of the SiV⁻ electronic spin coherence by 5 orders of magnitude by operating at temperatures below 500 mK. By aligning the magnetic field along the SiV⁻ symmetry axis, we demonstrate spin-conserving optical transitions and single-shot readout of the SiV⁻ spin with 89% fidelity. Coherent control of the SiV⁻ spin with microwave fields is used to demonstrate a spin coherence time T₂ of 13 ms and a spin relaxation time T₁ exceeding 1 s at 100 mK. These results establish the SiV⁻ as a promising solid-state candidate for the realization of quantum networks.