  Quantum emitters in layered hexagonal boron nitride (hBN) have recently
attracted a great attention as promising single photon sources. In this work,
we demonstrate resonant excitation of a single defect center in hBN, one of the
most important prerequisites for employment of optical sources in quantum
information application. We observe spectral linewidths of hBN emitter narrower
than 1 GHz while the emitter experiences spectral diffusion. Temporal
photoluminescence measurements reveals an average spectral diffusion time of
around 100 ms. On-resonance photon antibunching measurement is also realized.
Our results shed light on the potential use of quantum emitters from hBN in
nanophotonics and quantum information.
