Tapered nanowire antennas have emerged as a versatile solid-state platform for quantum optics. These broadband photonic structures efficiently funnel the spontaneous emission of an embedded quantum dot into a directive free-space beam. They find application in the realization of bright sources of quantum light, and enable the implementation of giant optical non-linearities, at the single-photon level.
In this work, we discuss advances aiming at further optimizing this light-matter interface. In particular, recent measurements revealed that the thermal excitation of a single nanowire vibration mode can have a sizeable influence on the quantum dot optical linewidth. This motivated a comprehensive theoretical analysis, which shows that the thermally-driven vibrations of the nanowire have a major impact on the quantum dot light emission spectrum. Even at liquid helium temperatures, these prevent the emission of indistinguishable photons. To overcome this intrinsic limitation, we propose several designs that restore photon indistinguishability thanks to a specific engineering of the mechanical properties of the nanowire. We anticipate that such a mechanical optimization will also play a key role in the development of other high-performance light-matter interfaces based on nanostructures.
We demonstrate photon-pair generation via spontaneous parametric down-conversion (SPDC) from two types of metasurfaces composed by AlGaAs nanocylinders: 1) monolithically fabricated on a selectively oxidized layer of AlAs epitaxially grown on a GaAs wafer; 2) fabricated by reporting the AlGaAs nanostructures on a transparent wafer via wafer bonding. In these samples, we observed SPDC both in back- and forward-scattering configurations, under excitation with a CW pump around 775 nm and single-photon detection on the signal and idler channels. The Bragg modulation of Mie-resonances enables paraxial SPDC, which demonstrates the potential of all-dielectric metasurfaces for quantum applications like on-axis quantum imaging.