Spatially entangled photon-pairs from lithium niobate nonlocal metasurfaces

TL;DR

This paper demonstrates the generation of spatially entangled photon pairs using a lithium niobate metasurface with nonlocal resonances, achieving high photon-pair rates and enabling miniaturized quantum devices.

Contribution

It introduces a novel metasurface-based method for producing spatially entangled photons with enhanced rates and tunable emission, advancing quantum photonics technology.

Findings

Photon-pair rate increased by 450 times

Violation of classical Cauchy-Schwartz inequality observed

Coincidence to accidental ratio reached 5000

Abstract

Metasurfaces consisting of nano-scale structures are underpinning new physical principles for the creation and shaping of quantum states of light. Multi-photon states that are entangled in spatial or angular domains are an essential resource for quantum imaging and sensing applications, however their production traditionally relies on bulky nonlinear crystals. We predict and demonstrate experimentally the generation of spatially entangled photon pairs through spontaneous parametric down-conversion from a metasurface incorporating a nonlinear thin film of lithium niobate. This is achieved through nonlocal resonances with tailored angular dispersion mediated by an integrated silica meta-grating, enabling control of the emission pattern and associated quantum states of photon pairs by designing the grating profile and tuning the pump frequency. We measure the correlations of photon positions and identify their spatial anti-bunching through violation of the classical Cauchy-Schwartz inequality, witnessing the presence of multi-mode entanglement. Simultaneously, the photon-pair rate is strongly enhanced by 450 times as compared to unpatterned films due to high-quality-factor metasurface resonances, and the coincidence to accidental ratio reaches 5000. These results pave the way to miniaturization of various quantum devices by incorporating ultra-thin metasurfaces functioning as room-temperature sources of quantum-entangled photons.