Effect of Spectral Diffusion on the Coherence Properties of a Single Quantum Emitter in Hexagonal Boron Nitride

Quantum emitters capable of producing single photons on-demand with high color purity are the building blocks of emerging schemes in secure quantum communications, quantum computing, and quantum metrology. Such solid-state systems, however, are usually prone to effects of spectral diffusion (SD), i.e., fast modulation of the emission wavelength due to the presence of localized, fluctuating electric fields. Two-dimensional materials are especially vulnerable to SD by virtue of the proximity of the emitters to the outside environment. In this study we report measurements of SD in a single hexagonal boron nitride (hBN) quantum emitter on the nanosecond to second time scales using photon correlation Fourier spectroscopy. We demonstrate that the spectral diffusion dynamics can be modeled by a two-component Gaussian random jump model, suggesting multiple sources of local fluctuations. We provide a lower limit of ∼0.13 for the ratio of the emitter's coherence time (T₂) to twice its radiative lifetime (2T₁) when it is measured on submicrosecond time scales. These results suggest that attaining transform-limited line widths could be achieved with moderate enhancement of the radiative rate. Moreover, the complex SD dynamics identified in our work inspires further exploration of the dephasing mechanisms in hBN as a viable quantum emitter platform.