# Spontaneous photon-pair generation at the nanoscale

## TL;DR

This paper demonstrates the first nanoscale generation of two-photon quantum states using a crystalline AlGaAs nanoantenna, achieving high efficiency at telecommunication wavelengths, with potential for advanced quantum communication and sensing.

## Contribution

It introduces a novel nanoscale photon-pair source based on spontaneous parametric down-conversion in a crystalline nanoantenna, surpassing conventional sources in efficiency.

## Key findings

- Photon-pair generation rate of 35 Hz at telecommunication wavelengths
- Normalized rate of 1.4 GHz/Wm, exceeding traditional sources
- Potential for multiplexing antennas for complex quantum states

## Abstract

Optical nanoantennas have shown a great capacity for efficient extraction of photons from the near to the far-field, enabling directional emission from nanoscale single-photon sources. However, their potential for the generation and extraction of multi-photon quantum states remains unexplored. Here we demonstrate experimentally the nanoscale generation of two-photon quantum states at telecommunication wavelengths based on spontaneous parametric down-conversion in an optical nanoantenna. The antenna is a crystalline AlGaAs nanocylinder, possessing Mie-type resonances at both the pump and the bi-photon wavelengths and when excited by a pump beam generates photonpairs with a rate of 35 Hz. Normalized to the pump energy stored by the nanoantenna, this rate corresponds to 1.4 GHz/Wm, being one order of magnitude higher than conventional on-chip or bulk photon-pair sources. Our experiments open the way for multiplexing several antennas for coherent generation of multi-photon quantum states with complex spatial-mode entanglement and applications in free-space quantum communications and sensing.