  Atomically thin van der Waals crystals have recently enabled new scientific
and technological breakthroughs across a variety of disciplines in materials
science, nanophotonics and physics. However, non-classical photon emission from
these materials has not been achieved to date. Here we report room temperature
quantum emission from hexagonal boron nitride nanoflakes. The single photon
emitter exhibits a combination of superb quantum optical properties at room
temperature that include the highest brightness reported in the visible part of
the spectrum, narrow line width, absolute photo-stability, a short excited
state lifetime and a high quantum efficiency. Density functional theory
modeling suggests that the emitter is the antisite nitrogen vacancy defect that
is present in single and multi-layer hexagonal boron nitride. Our results
constitute the unprecedented potential of van der Waals crystals for
nanophotonics, optoelectronics and quantum information processing.
