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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.

Parity-time (PT) symmetry has attracted considerable attention since optics was realized with the ability to provide a fertile platform for the exploration of PT symmetry. Although many of the previous researches on PT symmetry have been conducted in solid-state system and the network of fiber loops, coherent atomic medium offers another platform for the exploration of PT symmetry due to its easy reconfigurability and flexible tunability in parameters. This dissertation mainly focuses on the investigations of the phenomena related to PT-symmetric optical lattice in a coherent atomic medium. First, a controllable photonic crystal with periodic Raman gain was constructed in a coherent atomic medium. The dependence of the periodic Raman gain on the temperature of the atomic medium and total power of the pump beams has been investigated. Second, a new scheme to observe the PT-symmetric optical lattice in a coherent atomic medium was realized in experiment. The phase difference between the gain and loss waveguides was measured and the phase transition point was observed. Last, integer and fractional Talbot effects from PT-symmetric optical lattice, quasi-PT-symmetric optical lattices, and conventional electromagnetically induced transparency (EIT) optical lattice have been investigated. We find the intensity of the diffracted signal wave from the PT-symmetric optical lattice and quasi-PT -symmetric optical lattices can be substantially increased due to the gain channels in the optical lattice, while for the conventional EIT optical lattice, the intensity of the diffracted wave is decreased because of the absorption in the optical lattice. Moreover, the visibilities of the fractional Talbot image from the PT-symmetric optical lattice and quasi-PT-symmetric optical lattices are larger than that from the conventional EIT optical lattice for most of the propagation distances.

Metamaterials are artificially structured materials that are engineered to interact with waves in extraordinary ways, leading to unconventional physical phenomena not found in natural materials, such as negative refraction and cloaking. So far, they have been for the most part based on structures that are inherently symmetric upon time reversal. In this work, I will explore the largely uncharted properties of electromagnetic and acoustic metamaterials that are designed to purposely break time-reversal symmetry. I will show how time-reversal symmetry breaking can be exploited to build a novel class of non-reciprocal acoustic and electromagnetic devices, such as isolators and circulators. These devices will then be used as building blocks to construct the acoustic equivalent of topological insulators, a metamaterial that supports one-way phononic transport on its edges with strong topological protection against defects and disorder. I will study the exceptional properties of time-asymmetric systems that fulfill a special kind of space-time symmetry, consisting in taking their mirror image and running time backwards. Known as Parity-Time (PT) symmetry, this property leads to anomalous scattering behaviors, such as unidirectional invisibility and phase compensation. I will demonstrate theoretically and experimentally how PT-symmetric metasurface pairs can replicate electromagnetic phenomena usually associated with bulk metamaterials, including negative refraction, planar focusing and invisibility effects, with the clear advantage of being completely loss-immune and potentially overcoming the bandwidth limitations of passive metamaterials.

Metamaterials are artificially structured materials that are engineered to interact with waves in extraordinary ways, leading to unconventional physical phenomena not found in natural materials, such as negative refraction and cloaking. So far, they have been for the most part based on structures that are inherently symmetric upon time reversal. In this work, I will explore the largely uncharted properties of electromagnetic and acoustic metamaterials that are designed to purposely break time-reversal symmetry. I will show how time-reversal symmetry breaking can be exploited to build a novel class of non-reciprocal acoustic and electromagnetic devices, such as isolators and circulators. These devices will then be used as building blocks to construct the acoustic equivalent of topological insulators, a metamaterial that supports one-way phononic transport on its edges with strong topological protection against defects and disorder. I will study the exceptional properties of time-asymmetric systems that fulfill a special kind of space-time symmetry, consisting in taking their mirror image and running time backwards. Known as Parity-Time (PT) symmetry, this property leads to anomalous scattering behaviors, such as unidirectional invisibility and phase compensation. I will demonstrate theoretically and experimentally how PT-symmetric metasurface pairs can replicate electromagnetic phenomena usually associated with bulk metamaterials, including negative refraction, planar focusing and invisibility effects, with the clear advantage of being completely loss-immune and potentially overcoming the bandwidth limitations of passive metamaterials.