A solid state ultrabright source of entangled photon pairs

We demonstrate the fabrication of highly efficient sources of entangled photon pairs by inserting a semiconductor quantum dot in an optical cavity. Two electron-hole pairs trapped in a quantum dot (QD) radiatively recombine emitting a cascade of two polarization entangled photons. To extract both photons, we use a photonic molecule consisting of two identical micropillars, one empty, the other embedding a chosen QD. By adjusting the diameter of the pillars and their relative distance, we ensure that both optical transitions of the QD are simultaneously resonant to cavity modes. The emitted photon pairs are efficiently extracted thanks to Purcell effect. Doing so, we obtain the brightest sources of entangled photon pairs to date. We further show that the implementation of Purcell effect allows increasing the fidelity of the two photon state by reducing spin induced phase shift during the radiative cascade.