Excited States in the Si G-center from First-Principles GW/BSE Calculations

Defects in solid state materials have been identified as candidates for scalable qubits that can be grown on a chip. In diamond structure Si, the G-center—a pair of substitutional C atoms with an interstitial Si atom—has seen particular interest because of its optical activity. A zero-phonon line (ZPL) emission at 968 meV is observed in the O-band of optical telecommunication wavelengths, making it ideal for quantum information infrastructure. Emissions from the Si G-center are therefore compatible with optical fiber technology, which could make Si a material used for long distance coherent transmission in photonics and quantum optics. We investigate the excited states of the Si G-center with the GW approximation and the Bethe-Salpeter Equation (BSE) approach. We calculate the excitation energy, wavefunction character, and transition dipole moments associated with the first few excited states, using the open-source code BerkeleyGW. We consider the implications of the results for single photon emission and quantum technologies.