A photon source comprising: a quantum dot (21) having a first confined energy level capable of being populated with an electron and a second confined energy level capable of being populated by a hole; and supply means (23) for supplying carriers to the said energy levels, wherein the supply means are configured to supply a predetermined number of carriers to at least one of the energy levels to allow recombination of a predetermined number of carriers in said quantum dot to emit at least one photon.