Generation of a two-photon state from a quantum dot in a microcavity

We propose and characterize a two-photon (2P) source that emits in a highly polarized, monochromatic and directional beam, realized by means of a quantum dot embedded in a linearly polarized cavity. In our scheme, the cavity frequency is tuned to half the frequency of the biexciton (two excitons with opposite spins) and largely detuned from the excitons thanks to the large biexciton binding energy. We show how the emission can be Purcell enhanced by several orders of magnitude into the 2P channel for available experimental systems.