Enhanced entangled-photon-pair interaction with metallic nanoparticles

In recent years, many quantum lights-based applications were suggested, ranging from encrypted communication and precision metrology to fluorescent biomolecules detection and advanced spectroscopy schemes. Such applications mostly rely on entanglement, the property of correlations between particles which cannot be explained by classical mechanisms, to overcome classical light limitations. Some of these applications, e.g. nonlinear spectroscopy, require the use of entangled-photon-pair interaction (EPPI) with the matter. However, such entangled pairs, generated through spontaneous parametric down-conversion (SPDC), are scarce, and multi-photon interaction with matter is usually very weak and barely detectable. Therefore, an enhancement of this interaction is needed. In our research, we investigate a novel way to achieve such enhanced EPPI using metallic nanoparticles (MNPs), which are known for their exceptional capability of light-matter coupling at their localized surface plasmon resonance (LSPR). We present a novel way of theoretically estimating the rate of EPPI with MNPs, based on a simple method of classical light second-harmonic generation (SHG) measurements. The theory is supported with experimental results, obtained for a solution of silver NPs (SNPs). These results show an estimated six orders-of-magnitude EPPI enhancement, relative to the best organic molecules, and indicate that the use of SNPs can be advantageous for realization of advanced quantum light applications.