Efficient Sources of Entangled Photon Pairs Based on Deterministic Quantum Dot Microlenses

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In this project, we will develop deterministic and ultra-bright sources of polarization entangled photon pairs by combining the advantages of In(Ga)As QD grown on (111) oriented GaAs substrate, in-situ cathodoluminescence lithography (CLL) of monolithically integrated microlenses, and resonant excitation schemes. These quantum light sources are key elements of advanced quantum communication schemes, such as the quantum repeater, which are based on entanglement distribution. In our concept, single (111) QDs in the active region of the sources will enable the generation of polarization-entangled photon-pairs via the biexciton (XX) - exciton (X) radiative cascade because of their specific electronic structure of these QDs with diminishing fine-structure splitting. Using CLL, such QDs will be deterministically integrated into microlenses which, in combination with lower mirror section, ensure broadband enhancement of XX and X emission with a predicted extraction efficiency beyond 80 %. The full potential of these quantum light sources will be explored by resonant excitation schemes aiming at the on-demand emission of polarization entangled photon pairs with record brightness and indistinguishability. To this end, the high potential of our concept in the field of quantum communication will be demonstrated by performing two-photon interference experiments of emission from separated sources under resonant two-photon pi-pulse excitation.