Sunlight-excited spontaneous parametric down-conversion for ghost imaging

Ghost imaging (GI) has been under development for several years and is now achievable in both single- and multiphoton regimes with both quantum and classical light. Here, we address the experimental challenge of using sunlight as a pump beam to excite spontaneous parametric down-conversion and generate photon pairs. Remarkably, our investigations reveal that photon pairs excited from sunlight exhibit strong positional correlation, enabling their application in GI with an efficiency comparable to that achieved using a laser with similar pump power. This finding demonstrates the potential of employing an incoherent beam as the pump source in GI systems. Our research holds substantial significance as it expands the range of viable illumination sources—including scattered light and nontraditional artificial incoherent light—for imaging applications. A key potential use is in space-based quantum information systems, where this approach enables operation independent of laser sources.