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.
\r\n\r\nIn 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.
", "doi": "10.7907/j0x1-5742", "publication_date": "2026", "thesis_type": "phd", "thesis_year": "2026" }, { "id": "thesis:17264", "collection": "thesis", "collection_id": "17264", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05222025-165729471", "primary_object_url": { "basename": "pham_kim_2024_thesis-final.pdf", "content": "final", "filesize": 41860246, "license": "other", "mime_type": "application/pdf", "url": "/17264/1/pham_kim_2024_thesis-final.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Application of Ultrafast Spectroscopy Techniques to Probe Correlated Ion Hopping Mechanisms in Solid-State Ion Conductors", "author": [ { "family_name": "Pham", "given_name": "Kim Hoang", "orcid": "0000-0003-4053-6363", "clpid": "Pham-Kim-Hoang" } ], "thesis_advisor": [ { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" }, { "family_name": "See", "given_name": "Kimberly", "orcid": "0000-0002-0133-9693", "clpid": "See-Kimberly" } ], "thesis_committee": [ { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" }, { "family_name": "Stoltz", "given_name": "Brian M.", "orcid": "0000-0001-9837-1528", "clpid": "Stoltz-B-M" }, { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" }, { "family_name": "See", "given_name": "Kimberly", "orcid": "0000-0002-0133-9693", "clpid": "See-Kimberly" }, { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Superionic conductors, or solid-state ion conductors that surpass the ionic con- ductivity of its liquid counterpart, can enable more energy dense batteries, robust artificial ion pumps, and optimized fuel cells. The mechanisms enabling superionic conductivity still remain elusive, though many-body correlations between the mi- grating ions, lattice vibrational modes, and charge screening clouds have all been posited to greatly enhance ionic conduction. Most spectroscopic techniques cannot directly probe and validate the role of such correlations due to their inability to transiently resolve these ultrafast dynamics occurring at picosecond timescales. In this work, we develop an ultrafast technique that measures the time-resolved change in impedance while a light source ranging from UV to THz frequencies selectively excites an ion-coupled correlation. The technique is used to compare the relative changes in impedance of a solid-state Li\u207a conductor Li0.5La0.5TiO3 (LLTO) before and after light excitation to elucidate the role of charge screening clouds, optical phonons, and acoustic phonons on ion migration. From our techniques, we deter- mine that electronic screening and rocking phonon-mode interactions significantly dominate the ion migration pathway of LLTO compared to acoustic phonons. Al- though we only present one case study, our technique can extend to O\u00b2\u207b, H\u207a, or other charge carrier transport phenomena where ultrafast correlations control transport. Furthermore, the temporal relaxation of the measured impedance can distinguish ion transport effects caused by many-body correlations, optical heating, correlation, and memory behavior.", "doi": "10.7907/825x-r459", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:17006", "collection": "thesis", "collection_id": "17006", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02192025-011837407", "type": "thesis", "title": "Development and Characterization of a Table-Top Laser-Produced Plasma Source for In-Situ and Time-Resolved Soft X-Ray Absorption Spectroscopy", "author": [ { "family_name": "Nimlos", "given_name": "Danika Katherine", "orcid": "0000-0002-5414-0039", "clpid": "Nimlos-Danika-Katherine" } ], "thesis_advisor": [ { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" } ], "thesis_committee": [ { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" }, { "family_name": "Atwater", "given_name": "Harry Albert", "orcid": "0000-0001-9435-0201", "clpid": "Atwater-H-A" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "X-ray absorption spectroscopy (XAS) has emerged as an indispensable tool in the fields of carbon capture and conversion, providing element-specific insights into electronic structure, oxidation states, and chemical bonding. Of particular interest are soft X-rays (SXRs), which can probe the X-ray water window, enabling detailed studies of carbon, nitrogen, and transition metal L-edges in aqueous environments. Traditionally, access to this technique and this energy range has been limited to large- scale facilities like synchrotrons and XFELs, which can only serve a small population of users in a given year. Furthermore, more complex techniques such as time-resolved and in-situ XAS are practically inaccessible to the majority of users. This thesis explores the development of a table-top laser-produced plasma (LPP) source based on a gaseous target to extend the reach of XAS techniques into laboratory settings. Such sources offer significant advantages in accessibility, flexibility, and cost, while advances in X-ray optics and detection systems have further enhanced their utility. The research presented here focuses on the utilization of gaseous LPP sources for both in-situ and time-resolved XAS, pushing the boundaries of table-top soft X-ray absorption capabilities.
\r\n\r\nKey achievements include exploration of the lower temporal limit of LPP sources for SXR emission, and the first demonstration of liquid-phase XAS measurements using a gaseous LPP source. Gas-phase measurements were also achieved using the system built in this work. Additionally, a novel UV-pump/SXR-probe technique was developed, enabling future time-resolved studies of charge transfer dynamics in transition metal oxides. These advances pave the way for detailed investigations of photodriven processes, interfaces, and catalytic mechanisms critical to carbon capture and conversion. By improving temporal resolution and expanding the scope of in-situ XAS techniques, this work addresses fundamental challenges in the field, bringing the power of synchrotron-like spectroscopy into everyday laboratories. Ultimately, the results presented here aim to democratize XAS, fostering a broader adoption of this technique in catalysis and materials research.
", "doi": "10.7907/3e9t-xr72", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:17245", "collection": "thesis", "collection_id": "17245", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05192025-200240351", "primary_object_url": { "basename": "Hwang_Emily_thesis_V1.pdf", "content": "final", "filesize": 97652885, "license": "other", "mime_type": "application/pdf", "url": "/17245/1/Hwang_Emily_thesis_V1.pdf", "version": "v7.0.0" }, "type": "thesis", "title": "Nonlinear Frequency Conversion in Lithium Niobate Nanophotonic Circuits for Quantum Spectroscopy", "author": [ { "family_name": "Hwang", "given_name": "Emily Yoonju", "orcid": "0000-0002-9541-5887", "clpid": "Hwang-Emily-Yoonju" } ], "thesis_advisor": [ { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" } ], "thesis_committee": [ { "family_name": "Falson", "given_name": "Joseph", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Marandi", "given_name": "Alireza", "orcid": "0000-0002-0470-0050", "clpid": "Marandi-A" }, { "family_name": "Vahala", "given_name": "Kerry J.", "orcid": "0000-0003-1783-1380", "clpid": "Vahala-K-J" }, { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" } ], "local_group": [ { "literal": "Kavli Nanoscience Institute" }, { "literal": "div_eng" } ], "abstract": "Quantum light sources are becoming an increasingly popular alternative to pulsed lasers for spectroscopy, microscopy, and sensing. The inherent quantum correlations of entangled photons present unique advantages in spectroscopy, enabling high signal-to-noise ratios, low excitation fluxes, and time-resolved measurements without requiring a pulsed laser. Entangled photon sources for spectroscopic measurements typically consist of bulk crystals or ion-diffused waveguides. Integrated platforms such as thin-film lithium niobate have potential for highly efficient, tailored, and compact entangled photon sources through periodically poled nanophotonic waveguides. The advantageous nonlinear optical properties of lithium niobate coupled with the nanophotonic thin film platform allows for frequency conversion, quantum state generation, state manipulation, and sample interaction all on a single compact chip, demonstrating thin-film lithium niobate's potential for compact and portable integrated spectrometers.
\r\n\r\nHere, we present our work in frequency conversion and sample interactions in thin-film lithium niobate. Most of the previous demonstrations of nanophotonic lithium niobate waveguides have focused on infrared wavelengths for applications in quantum communication and computing, leaving the shorter wavelengths that are of interest for spectroscopy still a largely unexplored space. In this work, frequency conversion in thin-film lithium niobate is investigated from ultraviolet through telecom wavelengths. Periodically poled lithium niobate nanophotonic waveguides are fabricated for second harmonic generation in the ultraviolet-A region and entangled photon generation at visible and near-infrared wavelengths. Using a violet continuous wave laser, a waveguide with a fluorescent dye-doped polymer cladding layer is investigated for sample interactions. Finally, preliminary work in entangled photon triplet generation down to telecom wavelengths is explored. This work represents a step towards compact, on-chip spectrometers and sensors through lithium niobate photonic integrated circuits.
", "doi": "10.7907/895c-5s83", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:16303", "collection": "thesis", "collection_id": "16303", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02262024-021912071", "primary_object_url": { "basename": "he_manni_2024_thesis_submit.pdf", "content": "final", "filesize": 31075794, "license": "other", "mime_type": "application/pdf", "url": "/16303/2/he_manni_2024_thesis_submit.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Entanglement-Enhanced Bioimaging and Sensing", "author": [ { "family_name": "He", "given_name": "Manni", "orcid": "0009-0001-4237-900X", "clpid": "He-Manni" } ], "thesis_advisor": [ { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" } ], "thesis_committee": [ { "family_name": "Wei", "given_name": "Lu", "orcid": "0000-0001-9170-2283", "clpid": "Wei-Lu" }, { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" }, { "family_name": "Hong", "given_name": "Elizabeth J.", "orcid": "0000-0003-3866-418X", "clpid": "Hong-Elizabeth-J" }, { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Studies of entangled light-matter interactions have been gaining momentum because of their potential applications in bioimaging and sensing. Entangled photons are predicted to linearize nonlinear optical processes and offer orders of magnitude of enhancement to the interaction cross sections. To investigate the validity of entanglement-enhanced bioimaging techniques, a continuous wave (CW)-powered, on-chip, broadband entangled light source based on periodically poled lithium tantalate (ppLT) was designed and characterized. This light source achieved femtosecond entangled correlation times comparable to classical ultrafast lasers with an unprecedented power of ~100 nW in near-infrared (NIR), which is a crucial first step toward fully integrated, thin-film lithium niobate (TFLN)-based, visible to NIR entangled photon sources. This light source was then used for subsequent spectroscopy/microscopy experiments to systematically investigate the feasibility of entanglement-enabled microscopy techniques such as entangled two-photon absorption (ETPA) microscopy and entangled fluorescence lifetime measurements. A novel method was developed to measure fluorescence from ETPA using a spectrotemporally resolved Michelson interferometer which is good at eliminating false signals due to one-photon absorption and scattering. Careful experimental attempts at detecting virtual-state mediated ETPA from rhodamine 6G (R6G) and resonance-enhanced ETPA from indocyanine green (ICG) were made, and the ETPA signals were found to be below the instrument detection limits and often masked by one-photon effects such as scattering and linear absorption. Instead, experimental upper bounds were placed on the ETPA cross sections of the studied molecules, with an emphasis on continued improvement of the light source and instrument detection limits. On-chip entangled fluorescence lifetime imaging microscopy (entangled-FLIM) has also been identified as a new future development focus. The feasibility of the technique was demonstrated via a proof-of-principle experiment which measured the fluorescence lifetime of ICG in various solvents. Using entangled photons produced from a CW laser, the lifetime measurement scheme achieved a temporal resolution of 50 ps and a minimum measurable lifetime of 365 ps, which can be used to distinguish most biologically relevant fluorophores in the corresponding wavelength range. This experiment is a critical first step toward scalable, high-throughput, wavelength-multiplexed, and on-chip FLIM or lifetime measurements which could be used in label-free health monitoring technologies.", "doi": "10.7907/3zg0-4135", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "id": "thesis:16151", "collection": "thesis", "collection_id": "16151", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:08032023-213853772", "primary_object_url": { "basename": "Hickam_Bryce_2023.pdf", "content": "final", "filesize": 28267294, "license": "other", "mime_type": "application/pdf", "url": "/16151/1/Hickam_Bryce_2023.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Exploring How Entangled Photon Correlations Can Enhance Spectroscopy", "author": [ { "family_name": "Hickam", "given_name": "Bryce Patrick", "orcid": "0000-0003-2120-4769", "clpid": "Hickam-Bryce-Patrick" } ], "thesis_advisor": [ { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" } ], "thesis_committee": [ { "family_name": "Hadt", "given_name": "Ryan G.", "orcid": "0000-0001-6026-1358", "clpid": "Hadt-Ryan-G" }, { "family_name": "See", "given_name": "Kimberly", "orcid": "0000-0002-0133-9693", "clpid": "See-Kimberly" }, { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" }, { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" } ], "local_group": [ { "literal": "div_chem" } ], "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.
\r\n\r\nDespite 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.
", "doi": "10.7907/ez5h-qp07", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "id": "thesis:16375", "collection": "thesis", "collection_id": "16375", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05082024-165921385", "type": "thesis", "title": "Measuring Charge Carrier and Structural Photodynamics at Solar Energy Material Surfaces Using Transient Extreme Ultraviolet Reflection Spectroscopy", "author": [ { "family_name": "Michelsen", "given_name": "Jonathan Malte Zschiegner", "orcid": "0000-0002-7420-5610", "clpid": "Michelsen-Jonathan-Malte-Zschiegner" } ], "thesis_advisor": [ { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" } ], "thesis_committee": [ { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "See", "given_name": "Kimberly", "orcid": "0000-0002-0133-9693", "clpid": "See-Kimberly" }, { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Electronic and vibrational degrees of freedom, and their interactions, control the chemical and physical properties of solids. Core-level spectroscopies, such as transient extreme ultraviolet (XUV) spectroscopy, provide detailed information on the electronic structure and local coordination environment of a material. In this work, we employ transient XUV reflection spectroscopy to measure surface carrier and structural dynamics in solar energy materials. To interpret experimental spectra, excited state valence effects are incorporated into the OCEAN code (Obtaining core excitations from ab initio electronic structure and the NIST Bethe-Salpeter equation solver). The modeling of core-level spectra from first principles enables the extraction of carrier kinetics via the robust assignment of spectral features. Moreover, this thesis explores experimental and theoretical methods for understanding carrier-structural coupling in solids relevant to solar energy applications.
\r\n\r\nSpecifically, we explore the chemical and physical information contained in core-level spectra for various solar energy material systems and present guiding principles for designing a core-level electronic spectroscopy experiments to determine photoexcited carrier and structural dynamics. We report on experimental measurements of ultrafast surface carrier and structural dynamics in photocathodes zinc telluride and copper iron oxide. Further, complementary excited state theory is presented to extract excited state valence dynamics from experimental core-level spectra based on ground state implementations of the Bethe-Salpeter equation.
", "doi": "10.7907/73h7-kg35", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "id": "thesis:15078", "collection": "thesis", "collection_id": "15078", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:12132022-201432142", "primary_object_url": { "basename": "thesis_final.pdf", "content": "final", "filesize": 184003401, "license": "other", "mime_type": "application/pdf", "url": "/15078/3/thesis_final.pdf", "version": "v6.0.0" }, "type": "thesis", "title": "Understanding the Origins of Photoexcited XUV Spectra", "author": [ { "family_name": "Klein", "given_name": "Isabel McMillan", "orcid": "0000-00016134-6732", "clpid": "Klein-Isabel-McMillan" } ], "thesis_advisor": [ { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" } ], "thesis_committee": [ { "family_name": "Hadt", "given_name": "Ryan G.", "orcid": "0000-0001-6026-1358", "clpid": "Hadt-Ryan-G" }, { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" }, { "family_name": "Fu", "given_name": "Gregory C.", "orcid": "0000-0002-0927-680X", "clpid": "Fu-G-C" }, { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "A full measurement of photoexcited dynamics, from excitation to recombination, is required to understand the photochemical processes at the heart of solar energy materials and devices. Measuring these complete dynamics is often unachievable with a single experimental tool. Transient X-ray spectroscopies, however, have proven to be powerful techniques as they can separately measure electron and hole dynamics, as well as vibrational and structural modes, all with elemental specificity. The interpretation of these measurements is still challenging, as the core-hole created following a core-level transition distorts the measured spectrum. This thesis aims to develop complementary experimental and computational techniques to measure and interpret transient X-ray spectra. Initially, the measured photoexcited dynamics of ZnTe and CuFeO\u2082, which reveal polaron formation and lattice coupling, as well as electron and hole kinetics and band gap dynamics, are presented. Following this experimental work, we develop an ab initio computational method for modeling transient X-ray and extreme ultraviolet (XUV) spectra. The ab initio method is a Bethe-Salpeter equation (BSE) approach based on the previously developed Obtaining Core Excitations from Ab initio electronic structure and the NIST BSE solver (OCEAN) code. Building on the foundations of the OCEAN code, we incorporate photoexcited states for a range of transition metal oxides and demonstrate the method\u2019s ability to simulate the effects of state filling, isotropic thermal expansion and polaron states on XUV absorption spectra. Importantly, our method is also able to fully decompose the calculated spectra into the constituent components of the X-ray transition Hamiltonian, providing further insight into the origins and nature of spectral features. The XUV absorption spectra for the ground, photoexcited, and polaron states of \u03b1-Fe\u2082O\u2083, as well as for the ground, photoexcited, and thermally expanded states of other first row transition metal oxides \u2013 TiO\u2082, \u03b1-Cr\u2082O\u2083, \u03b2-MnO\u2082, Co\u2083O\u2084, NiO, CuO, and ZnO \u2013 are calculated to demonstrate the accuracy of our approach. This method is easily generalized to K, L, M, and N edges to provide a general approach for analyzing transient X-ray absorption or reflection data.
", "doi": "10.7907/s8qe-4s74", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" }, { "id": "thesis:14499", "collection": "thesis", "collection_id": "14499", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02162022-092446660", "type": "thesis", "title": "Entangled Photon Interferometry: Development of Photonic Systems Towards Quantum Spectroscopy", "author": [ { "family_name": "Szoke", "given_name": "Szilard", "orcid": "0000-0001-7860-4638", "clpid": "Szoke-Szilard" } ], "thesis_advisor": [ { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" } ], "thesis_committee": [ { "family_name": "Hadt", "given_name": "Ryan G.", "orcid": "0000-0001-6026-1358", "clpid": "Hadt-Ryan-G" }, { "family_name": "Minnich", "given_name": "Austin J.", "orcid": "0000-0002-9671-9540", "clpid": "Minnich-A-J" }, { "family_name": "Marandi", "given_name": "Alireza", "orcid": "0000-0002-0470-0050", "clpid": "Marandi-A" }, { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Entangled photon spectroscopy is an emergent field offering the potential to perform nonlinear and non-classical measurements at low photon fluxes. The entangled photon pairs which are generated using a continuous-wave laser pumped spontaneous parametric downconversion (SPDC) process simultaneously display strong correlations in time and anti-correlations in frequency space. Measuring changes in these correlations provides classical and non-classical information about the underlying dynamics and fluctuations of the sample-system. Further, because these two variables are not Fourier conjugates, entangled photon spectroscopy makes it possible to exploit the spectral resolution of continuous-wave lasers, while leveraging the temporal relationship of the near-simultaneously generated photon pairs which effectively mimics an ultrafast pulsed laser experiment. Nonlinear and ultrafast measurements can therefore be performed with low-power sources while also achieving superior signal-to-noise ratios due to the underlying quantum statistics. As photons in a pair can be separately manipulated, spectroscopic setups using these quantum states of light have marked benefits in contrast to measurements performed using traditional single photon states.
\r\n\r\nHere, we describe our efforts towards implementing quantum interferometers to test the abilities of entangled photon pairs in nonlinear spectroscopic studies. Specifically, we present work on the development of free-space, fiber-optic, and nanophotonic systems that leverage nonlinear materials to generate narrow to broadband entangled photon pairs via SPDC. The numerical methods used for designing and tailoring these entangled photon sources are outlined together with associated experimental limitations. The spectral-temporal correlations of the two-photon states are characterized using fourth-order interferometry, demonstrating Hong-Ou-Mandel interference with picoseconds to femtoseconds coherence times, and wavelengths ranging from the IR to the UV. A monolithic nanophotonics architecture is proposed for completely on-chip, entangled, ultrafast, and nonlinear spectroscopy.
", "doi": "10.7907/brct-zh28", "publication_date": "2022", "thesis_type": "phd", "thesis_year": "2022" } ]