Developing New Methods of Quantum Spectroscopy with Nonlinear Integrated Photonics

Citation

Harper, Nathan Andrew (2026) Developing New Methods of Quantum Spectroscopy with Nonlinear Integrated Photonics. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/j0x1-5742. https://resolver.caltech.edu/CaltechTHESIS:09052025-191750417

Abstract

Photon pairs produced through spontaneous parametric down-conversion exhibit entanglement in their time-energy degrees of freedom, offering sub-100 fs entanglement times while simultaneously exhibiting a joint energy resolution dictated by that of the continuous-wave pump laser. While entangled photon pairs have found many applications in sensing and imaging, taking advantage of their ultrafast correlations has proven to be more difficult.

In this dissertation, we advance a number of practical aspects of spectroscopy with entangled pairs of photons. First, we show that the ultrafast correlations in photon pairs are useful for fluorescence lifetime measurements, enabling a CW laser to perform time-resolved measurements through a simple heralding scheme. Next, we develop bright, efficient, and single spatial mode sources of entangled photons using thin-film lithium niobate nanophotonics, bringing these devices to the visible and near-IR for the first time. In the process, we develop a source of UV light and investigate the performance of thin-film lithium niobate for evanescent sensing. Finally, we show promising results that two down-conversion processes in the same waveguide can be cascaded to generate entangled photon triplets with high efficiency, enabling pairs of photons to be heralded.

Thesis Files