Multi-photon processes in solid-state quantum emitters

In order to stimulate these systems into emitting photons, lasers are used to excite them to high-level excited states. These states relax, and in doing so release photons. This is called quasi-resonant excitation. The problem with this quasi-resonant excitation procedure is that it also excites the semiconductor solid-state environment surrounding the quantum dot. This can couple to the quantum dot in unwanted ways, and cause it to emit two or more photons as it relaxes. These multiphoton processes degrade the quantum dot’s usefulness as a single photon source.