Long-lived entanglement of a spin-qubit register in silicon photonics

Color centers provide an optical interface to quantum registers based on electron and nuclear spin qubits in solids. The T center in silicon is an emerging spin-photon interface that combines telecom O-band optical transitions and a long-lived electron spin in a scalable photonics platform. In this work, we demonstrate the initialization, coherent control, and state readout of a three-qubit register based on the electron spin of a T center coupled to a hydrogen and a silicon nuclear spin. The spin register exhibits long spin echo coherence times of 0. 41 (2) ms for the electron spin, 112 (12) ms for the hydrogen nuclear spin, and 67 (7) ms for the silicon nuclear spin. We use nuclear-nuclear two-qubit gates to generate entanglement between the two nuclear spins with a fidelity of F=0. 77 (3) and a coherence time of T^*₂=2. 60 (8) ms. Our results show that T centers can realize a long-lived multi-qubit register with an optical interface in silicon photonics.