Abstract
We use frequency entangled photons, generated via spontaneous parametric down conversion, to measure the broadband spectral response of an array of gold nanoparticles exhibiting Fano-type plasmon resonance. Refractive index sensing of a liquid is performed by measuring the shift of the array resonance. This method is robust in excessively noisy conditions compared with conventional broadband transmission spectroscopy. Detection of a refractive index change is demonstrated with a noise level 70 times higher than the signal, which is shown to be inaccessible with the conventional transmission spectroscopy. Use of low photon fluxes makes this method suitable for measurements of photosensitive bio-samples and chemical substances.
Highlights
New insights into understanding the behavior of materials at the nanoscale and progress in nanofabrication capabilities have triggered great interest in the study of plasmonic nanostructures
We demonstrate advantages of using frequency-entangled photons, generated via spontaneous parametric down conversion (SPDC), in revealing the spectroscopic response of a plasmonic refractive-index sensor under noisy conditions
The pump is eliminated by a UV mirror, and the SPDC is split by a nonpolarizing beam splitter (NPBS)
Summary
New insights into understanding the behavior of materials at the nanoscale and progress in nanofabrication capabilities have triggered great interest in the study of plasmonic nanostructures. Plasmonic sensors benefit from their biocompatibility and high sensitivity [1,2,3,4]. With the sensitivity of the sensors approaching the atto-Molar scale, as well as sensing of photosensitive substances, it is important that the analyte is not damaged or modified by the probing light. For sensing with low-photon counts, the main practical issue is careful suppression of the influence of the background noise. This is challenging with conventional spectroscopy, but quantum optics can be exploited to effectively address this issue [5,6,7]
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