Narrowband Quantum Light Emission from Oxygen-Related Color Centers in Hexagonal Boron Nitride

Hexagonal boron nitride (hBN) is attracting increasing attention for quantum information science due to its ability to host carbon-related color centers that perform as robust, high-temperature quantum light sources, as well as native defects such as charged V_B^- centers with optically addressable spin states toward spin-based quantum applications. So far, achieving isolation of individual V_B^- defects out of ensemble emission remains difficult due to their low quantum yield, warranting the search for other candidates. Here, we show that oxygen annealing creates individual quantum emitters characterized by a phonon-sideband-free emission in the 800 nm band. The emission is strongly linearly polarized (79%), with a characteristic emission dipole rotation of 20° and a saturation intensity around 1 MHz, comparable to the brightest hBN quantum emitters reported previously. Their time dynamics appear free of spectral diffusion or blinking, implying excellent room-temperature photostability without additional passivation techniques. Detailed cryogenic studies estimate zero pump power line width down to 87.5 μeV, which is several orders of magnitude narrower compared to carbon-related or V_B^- defect center emission under nonresonant excitation. The demonstrated photophysical properties of oxygen-related quantum emitters are promising to advance free-space quantum communication and might enable indistinguishable single photons or interfacing with ⁸⁷Rb vapor-based quantum memory technologies in future work.