Spectrally stable defect qubits with no inversion symmetry for robust spin-to-photon interface.

Scalable spin-to-photon interfaces require quantum emitters with strong optical-transition dipole moment and low coupling to phonons and stray electric fields. It is known that particularly for coupling to stray electric fields, these conditions can be simultaneously satisfied for emitters that show inversion symmetry. Here, we show that inversion symmetry is not a prerequisite criterion for a spectrally stable quantum emitter. We find that identical electron density in ground and excited states can eliminate the coupling to the stray electric fields. Further, a strong optical-transition dipole moment is achieved in systems with altering sign of the ground and excited wave functions. We use density-functional perturbation theory to investigate an optical center that lacks inversion symmetry. Our results show that this system close to ideally satisfies the criteria for an ideal quantum emitter. Our study opens an additional rationale in seeking promising materials and point defects towards the realization of robust spin-to-photon interfaces.