Combining the long-coherence of spin qubits and the capability to transmit information and entanglement through photons, spin-photon interfaces (SPIs) are a promising platform for networked quantum computation and long-distance quantum communication. SPIs that possess local ‘memory’ qubits in addition to the optically coupled ‘communication’ qubit can improve remote entanglement fidelities through brokered entanglement schemes and entanglement purification. In these schemes, it is critical to protect the memory qubit from decoherence during entanglement operations on the communications qubit. Silicon, a platform with mature microelectronic and nanophotonic fabrication, is host to the $T$-center, an SPI with emission in the telecommunications O-band that directly integrates with silicon nanophotonics. Cavity-coupled $T$-centers are a platform for brokered entanglement distribution in silicon photonic circuits and over long-distance optical fiber links. The $T$-center's electron and nuclear spin qubits are an intrinsic register of communication and memory qubits respectively, with anisotropic hyperfine coupling. In this work we determine the $T$-center's hydrogen hyperfine coupling tensor. We also introduce schemes to protect against dephasing or eliminate relaxation of the $T$-center's hydrogen memory qubit during optical excitation. These results address a key challenge for practical $T$-center quantum networks.

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• Density functional theory
• Fine & hyperfine structure
• Nuclear & electron resonance
• Quantum engineering
• Quantum networks
• Single photon sources
• Spin coherence
• Spontaneous emission
• Zeeman effect
• Optically detected magnetic resonance