The C-center in silicon: an L-band emitter with memory

Silicon is a technologically mature material that has attracted renewed interest as a host for quantum defects. Its smaller band gap mainly enables excitonic states, nevertheless, stable emitters operating in the telecommunication wavelengths may exist in this material.

We report first-principles calculation results on a similar excitonic defect in silicon, the so-called C-center which emits in the L-band. We use HSE DFT to calculate its singlet ground state and to describe singlet and triplet excitons formed with the CBM. We validate our method by GW and BSE calculations. We also determine the hyperfine, dipolar spin-spin and spin-orbit interaction strengths in the excited triplet state, crucial for the manipulation of the qubit. We report the symmetry-allowed spin-orbit couplings in the triplet state, revealing an ISC preferentially populating the 0 sublevel, from where phosphorescence emission leads to the ground state. ODMR contrast emerges owing to the much longer lifetimes of the other magnetic levels as obtained in our calculations.

Based on these results, we detail quantum protocols for the initialization, storage and readout of the nuclear spin. Owing to the excited triplet state, the nuclear spin quantum memory is expected to show large coherence time.