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

Abstract: We experimentally demonstrate a violation of local realism with negligible spatial postselection on the 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 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 supports more than 45,000 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.