Deterministic generation of entangled photon pairs from a semiconductor quantum dot

Optical tuning based on the AC Stark effect is used to cancel the fine-structure splitting in a single self-assembled InAs quantum dot. Under this condition, polarization anisotropy vanishes, and photon pairs emitted from the biexcitonic radiative cascade become polarization-entangled. Entanglement is verified by well-known criteria applied to the two-photon density matrix that was reconstructed experimentally via quantum state tomography. Our approach uses a planar optical microcavity for efficient background laser discrimination, and yields triggered polarization-entangled photons deterministically.