Identifying single photon emitters
Antibunching is a characteristic of light with sub-Poissonian statistics. Observation of antibunching (by means of photon coincidence correlation or second-order correlation) for instance reveals whether there is only a single photon emitter present in a sample. The technique is very often employed in the characterization of single quantum systems such as single molecules, quantum dots, carbon nanotubes, and defect centers in diamond nanocrystals, or in applications based on single photons sources. Antibunching experiments can also reveal the degree of multimerization
The antibunching dip of the correlation function is based on the fact that a single emitter can only emit one photon at a time. The process can easily be described using a simpliﬁed two-level energy diagram, where a molecule in an excited state requires a ﬁnite amount of time before it relaxes back to the ground state by emitting a photon. The temporal separation between adjacent photons is therefore determined mostly by the excited-state lifetime. This effect is known as antibunching and represents the sub-Poissonian nature of the emitted light.