Coherent control of a ¹³C nuclear spin coupled to a tin-vacancy center in diamond

Robust quantum networks require a coherent interface between photons and long-lived spin qubits. The tin-vacancy center in diamond provides such an interface, combining excellent optical properties due to its inversion symmetry with a strong spin-orbit coupling that yields long electron spin lifetimes even at elevated temperatures. To achieve high-fidelity spin control while avoiding Ohmic heating, we fabricate a superconducting niobium coplanar waveguide on a diamond membrane. Using this platform, we realize optical initialization and coherent manipulation of both the electron and a nearby ¹³C nuclear spin. The nuclear spin can be initialized with 99 % fidelity and driven with a Rabi frequency of 13 kHz using only 10 dBm of RF power. Dynamical decoupling extends the nuclear coherence to 1.3 s, far exceeding the electron coherence of 10 ms. Additional randomized benchmarking confirms high-fidelity control of the nuclear spin with a single-qubit fidelity of 99.92 %. Together with the near-Fourier-limited optical transition, this electron-nuclear spin register enables long-lived quantum memories for optically connected SnV-based network nodes.