  Two-photon absorption is an important non-linear process employed for high
resolution bio-imaging and non-linear optics. In this work we realize
two-photon excitation of a quantum emitter embedded in a two-dimensional
material. We examine defects in hexagonal boron nitride and show that the
emitters exhibit similar spectral and quantum properties under one-photon and
two-photon excitation. Furthermore, our findings are important to deploy
two-dimensional hexagonal boron nitride for quantum non-linear photonic
applications.
