Quantum and classical frameworks form two perspectives for describing physical systems. Their formulation also presents interesting isomorphism: for example, the Schrodinger equation can find its classical correspondence in the paraxial Helmholtz equation, and coherent atomic population transfers is analogous to coupling dynamics in waveguides. In classical coupled mode systems, quantum notion can be manifested in the following ways: (1) adiabatic (i.e., sufficiently slow) evolution of the Hamiltonian enables robust mode conversion and light transfer, where the dynamics is carried out in predominantly one eigenmode; (2) non-Hermitian Hamiltonians give rise to peculiar singularities known as exceptional points (EPs), associated with not only degenerate eigenvalues but coalescent eigenvectors. In this dissertation, we explore the above principles in light manipulation, sensing, and photonic emulation. First, we numerically demonstrate two examples of photonic devices based on adiabatic evolution engineering. We present a coupled waveguide system analogous to the atomic physics process of stimulated Raman adiabatic passage, where the principle of adiabaticity not only allows high-extinction polarization mode splitting, but also counterintuitively mitigates the losses from the plasmonic structure involved. We show a modal hybridization effect in rib waveguide geometry that allows the mode to adiabatically evolve from one polarization to its orthogonal state upon electro-optic modulation in thin film lithium niobate, enabling an actively switchable polarization converter. We propose a generic EP emulator based on programmable photonics to tackle the challenging implementation of EP. Our approach combines on-chip operations of coupling, loss and detuning based on generic photonic modules (Mach-Zehnder interferometers), and a discrete scheme for mapping Hamiltonians to common mesh architecture. We demonstrate multiple exemplary EP functionalities, including loss-induced transparency, encircling second-order EPs in the PT and anti-PT symmetry picture, and a third-order EP. The proposed EP emulator marks a new paradigm for discrete, \textit{in situ} programming of EPs and multi-functional, repurposable EP devices. We also present our preliminary work on NV center-induced EPs. In contrast to conventional fluorescence-based schemes for addressing NV centers, we leverage NV centers' absorption to bring a coupled ring resonator system to an EP and numerically demonstrate the emerging dynamics. Our primary numerical results promise proof-of-concept magnetometry, combining NV centers' response to magnetic and microwave fields with the sensitivity enhancing nature of EP. This dissertation sheds light on unconventional photonics inspired by quantum-like principles. / 2025-08-29T00:00:00Z

Doctor of Philosophy / Department of Physics / B.D. DePaola / In recent years, coherent excitation techniques have focused on the ability to efficiently prepare atomic or molecular systems into a selected state. Such population control plays a key role in cutting-edge research taking place today, such as in the areas of quantum information and laser-controlled chemical reactions. Stimulated Raman adiabatic passage (STIRAP) is a widely-used coherent excitation technique that provides a relatively robust control mechanism for efficiently exciting a target population into a desired state. While the technique is well proven, current experimental techniques yield little information on the population dynamics taking place throughout the excitation process, and experimentalists rely solely on final excited-state measurements to determine the efficiency of population transfer. This dissertation presents a unique diagnostic tool to measure multilevel coherent population transfer on a short (nanosecond) timescale. The technique described here uses magneto-optical trap recoil ion momentum spectroscopy (MOTRIMS) as a noninvasive probe of a coherently-controlled system. It provides extremely detailed information about the excitation process, and highlights some important characteristics seen in excited populations that would otherwise be misleading or completely overlooked if one were to use more traditional diagnostic techniques. This dissertation discusses both the theoretical and experimental results applied to three-level coherently excited target populations of Rb-87.