Violation of local realism with spatially multimode parametric down-conversion pumped by spatially incoherent light

TL;DR

This paper demonstrates a violation of local realism using spatially multimode entangled photons generated by SPDC pumped with incoherent LED light, showing that coherent lasers are not necessary for entanglement generation.

Contribution

It experimentally shows that entanglement and violation of local realism can be achieved with incoherent light sources, expanding the potential for practical quantum technologies.

Findings

Achieved CHSH inequality violation of S=2.532 with multimode detection

Collected nearly 4,080 SPDC spatial modes in the experiment

Established that coherent pump sources are not required for entanglement

Abstract

We experimentally demonstrate a violation of local realism with highly spatially multimode polarization-entangled two-photon states produced by spontaneous parametric down-conversion (SPDC) pumped by a spatially incoherent light source-a light-emitting diode (LED). While existing studies have observed such a violation only by post-selecting the LED-pumped SPDC photons into a single spatial detection mode, we achieve a Clauser-Horne-Shimony-Holt inequality violation of $S = 2.532 \pm 0.069 > 2$ using a spatially multimode detection setup that collects nearly 4,080 SPDC spatial modes. These results indicate that coherent pump sources, such as lasers, are not required for SPDC-based entanglement generation. Our work could enable novel and practical sources of entangled photons for quantum technologies such as device-independent quantum key distribution and quantum-enhanced sensing.