Towards an accurate electronic structure of single photon emitters in hexagonal boron nitride

Understanding single photon emission from defects in hexagonal boron nitride (h-BN) is an essential yet challenging step towards further utilizing the material as a room-temperature quantum device. Here, we systematically examine potential luminescence candidates in h-BN using the full configuration interaction quantum Monte Carlo approach. With such a high-level treatment of electron correlation, we can finally determine the electronic states of all the defects studied, revealing high-spin ground states for quantum manipulation and correcting previous misunderstandings. Furthermore, by computing the low-lying electronic states and analyzing the corresponding many-body wave functions, we identify two potential sources for the mysterious luminescence band in the visible region, including a doublet-doublet transition. Our calculations shed light on the intricate correlated electronic states of single photon emitters in h-BN, and establish a reliable theoretical foundation for addressing other challenges beyond the electronic structure.