Exploring How Entangled Photon Correlations Can Enhance Spectroscopy

Citation

Hickam, Bryce Patrick (2024) Exploring How Entangled Photon Correlations Can Enhance Spectroscopy. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/ez5h-qp07. https://resolver.caltech.edu/CaltechTHESIS:08032023-213853772

Abstract

Quantum light sources consisting of highly correlated or "entangled" photon pairs are increasingly becoming popular alternatives to classical light sources to perform microscopy and spectroscopy. Entangled photon pairs can replicate and enhance spectroscopic signals and have practical advantages compared to the pulsed laser systems that are typically utilized to perform these measurements. For instance, entangled photons are inherently low-flux, enabling measurements to be performed without undesired photoeffects, such as sample heating and degredation or nonideal photoinduced sample behavior. In addition, entangled photon sources can be generated and manipulated on much smaller physical footprints than state-of-the-art pulsed laser systems with comparable frequency bandwidths and time resolutions. Together, these capabilities could allow for the development of spectroscopic instruments that do not rely on bulky, expensive pulsed laser systems that necessitate teams of specialists to maintain. In turn, this instrument development could enable more widespread access to exotic forms of atomic and material characterization.

Despite a growing body of theoretical work, the field of experimental entangled photon spectroscopy is still nascent and entangled light-matter interactions have yet to be fully characterized in laboratory settings. Here, we investigate entangled photon light-matter interactions towards the goal of developing entangled spectroscopic techniques. A broadband entangled photon source with femtosecond coherence times is designed and characterized to perform these measurements. Using this source and an entangled photon spectrometer, characterization of the entangled photon enhancement to two-photon absorption are attempted by in studies of two different molecular dyes, Rhodamine 6G and zinc tetraphenylporphyrin. The entangled photon two-photon absorption enhancement is determined to be below previously reported values due to the presence of single photon scattering signals. Finally, entangled photons are utilized to replicate fluorescence lifetime measurements using a continuous wave pump laser and the temporal correlations inherent to entangled photon pairs. As the first experimental demonstration of this technique, the fluorescence lifetimes of indocyanine green in three solvent systems are measured.

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