Theses and Dissertations from UMD
Permanent URI for this communityhttp://hdl.handle.net/1903/2
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
Browse
121 results
Search Results
Item INTEGRATION OF ATOMIC EMITTERS IN PHOTONIC PLATFORMS FOR CLASSICAL AND QUANTUM INFORMATION APPLICATIONS(2024) Zhao, Yuqi; Waks, Edo; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Integrated photonics provide a powerful toolbox for a wide range of classical and nonclassical applications. In addition to their scalability and significantly lower power consumption, integrated photonic structures enable new design knobs and functionalities that are inaccessible in their bulk counterparts.Solid-state atomic emitters, such as rare-earth ions (REIs) and quantum dots, serve as excellent sources for scalable quantum memories and exhibit strong nonlinear resonant absorption. Integrating atomic emitters with photonic devices enhances light-matter interactions, unlocking new opportunities for advanced optoelectronic systems in both classical and quantum regimes. This thesis tackles two main challenges utilizing the integration of photonic devices and atomic emitters: (1) developing scalable quantum network components, and (2) creating low-power nonlinear components for classical on-chip optical signal processing. Specifically, we focus on a platform of rare-earth ion doped thin-film lithium niobate (TFLN), leveraging the ions’ stable optical transitions with thin-film lithium niobate’s rich toolbox of high-performance photonics. We first demonstrate an integrated atomic frequency comb (AFC) memory in this platform, an essential component for quantum networks. This memory exhibits a broad storage bandwidth exceeding 100 MHz and optical storage time as long as 250 ns. As the first demonstrated integrated AFC memory, it features a significantly enhanced optical confinement compared to the previously demonstrated REI memories based on ion-diffused waveguides, leading to a three orders of magnitude reduction in optical power required for a coherent control. Next, we develop reconfigurable narrowband spectral filters using ring resonators in the REI:TFLN platform. These on-chip optical filters, with linewidths in the MHz and kHz range and extinction ratios of 13 dB – 20 dB, are crucial for reducing background noise in quantum frequency conversion. By spectral hole burning at 100 mK temperature in a critical-coupled resonance mode, we achieve bandpass filters with a linewidth of as narrow as 681 kHz. Moreover, the cavity enables reconfigurable filtering by varying the cavity coupling rate. Such versatile integrated spectral filters with high extinction ratio and narrow linewidth could serve as fundamental component for optical signal processing and optical memories on-a-chip. We also demonstrate picowatt-threshold power nonlinearity in TFLN, utilizing the strong resonant nonlinear absorption induced by three-level REIs and enhanced by TFLN ring resonators. This work presents three distinct nonlinear transmission functions by adjusting the ring’s coupling strength. The lifetime of the nonlinear transmission is measured to be ~3 ms, determined by the ion’s third-level lifetime. Finally, we propose a novel nonlinear device design based on a different material system and mechanism - an ultrathin optical limiter with low threshold intensity (0.45 kW/cm2), utilizing a 500 nm-thick GaAs zone plate embedded with InAs quantum dots. The optical limiting performance, enabled by the zone plate’s nonlinear focusing behavior, is investigated using FDTD simulations. We also explore the effects of the zone plate’s thickness and radius on its optical limiting performance.Item TOPOLOGICAL PHOTONICS: NESTED FREQUENCY COMBS AND EDGE MODE TAPERING(2024) Flower, Christopher James; Hafezi, Mohammad; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Topological photonics has emerged in recent years as a powerful paradigm for the designof photonic devices with novel functionalities. These systems exhibit chiral or helical edge states that are confined to the boundary and are remarkably robust against certain defects and imperfections. While several applications of topological photonics have been demonstrated, such as robust optical delay lines, quantum optical interfaces, lasers, waveguides, and routers, these have largely been proof-of-principle demonstrations. In this dissertation, we present the design and generation of the first topological frequency comb. While on-chip generation of optical frequency combs using nonlinear ring resonators has led to numerous applications of combs in recent years, they have predominantly relied on the use of single-ring resonators. Here, we combine the fields of linear topological photonics and frequency microcombs and experimentally demonstrate the first frequency comb of a new class in an array of hundreds of ring resonators. Through high-resolution spectrum analysis and out-of- plane imaging we confirm the unique nested spectral structure of the comb, as well as the confinement of the parametrically generated light. Additionally, we present a theoretical study of a new kind of valley-Hall topological photonic crystal that utilizes a position dependent perturbation (or “mass-term”) to manipulate the width of the topological edge modes. We show that this approach, due to the inherent topological robustness of the system, can result in dramatic changes in mode width over short distances with minimal losses. Additionally, by using a topological edge mode as a waveguide mode, we decouple the number of supported modes from the waveguide width, circumventing challenges faced by more conventional waveguide tapers.Item Development of Photonic Reservoir Computers for Radiofrequency Spectrum Awareness(2024) Klimko, Benjamin; Chembo, Yanne K.; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In this dissertation, we study the use of several optoelectronic oscillator architectures for physical reservoir computing tasks. While optoelectronic oscillator-based reservoir computers have been reported in the literature for over a decade, all reported experimental results have been processed using wideband systems with baseband data sets. Our work focuses on two majorinnovations for physical reservoir computing: (i) narrowband reservoir computers allowing computing tasks to be performed natively on radiofrequency signals and (ii) illustrating that “simplified” optoelectronic oscillators, without external optical modulators, are capable of meeting or exceeding the results from more complex photonic reservoir computers. By their nature, optoelectronic oscillators operate in the radio passband regime and reservoir computers have been shown to be capable on time-series tasks such as waveform prediction and classification data sets. We demonstrated that the optoelectronic oscillator-based reservoir computer can effectively process signals in the radio passband, which is a novel result that could provide an enabling technology for next-generation communication methods such as cognitive networks. The benefits of this innovation would scale with increasing frequency, such as potential use with millimeter-wave cellular networks. In our second physical reservoir innovation, we have shown that external optical modulators, nearly ubiquitous devices in optoelectronic oscillators, may be excluded from the design of a physical reservoir computer without decreasing its accuracy. This is a major result as a reservoir without active optical components could be built on a single integrated circuit using modern semiconductor manufacturing processes. Such integration and miniaturization would be a large step towards photonic reservoir systems that could be more easily put into an operational environment. Up to this point, there has been minimal work on transitioning the optoelectronic oscillator from a benchtop, experimental system to one useful in the real world. Lastly, we investigated the relationship between computational power of the reservoir computer and task error. This is a crucial finding since reservoir computing is often touted as an alternative computing paradigm that is less resource-intensive than other computing methods. By determining a threshold on computational needs for a photonic reservoir computer, we ensure that such systems are utilized efficiently and do not unnecessarily use resources.Item Ultracold Gases in a Two-Frequency Breathing Lattice(2024) Dewan, Aftaab; Rolston, Steven L; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Driven systems have been of particular interest in the field of ultracold atomic gases. Theprecise control and relative purity allows for construction of many novel Hamiltonians. One such system is the ‘breathing’ lattice, where both the frequency and amplitude is modulated in time, much like an accordion. We present the results of a phenomenological investigation of a proposed experiment, one where we apply a two-frequency breathing lattice to an atomic system. The results are surprising, as they indicate the possibility of a phase-dependent transition between nearest-neighbour and beyond nearest-neighbour interactions.Item Chiral light-matter interaction in fermionic quantum Hall systems(2024) Session, Deric Weston; Hafezi, Mohammad; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Achieving control over light-matter interactions is crucial for developing quantum technologies. This dissertation discusses two novel demonstrations where chiral light was used to control light-matter interaction in fermionic quantum Hall systems. In the first work, we demonstrated the transfer of orbital angular momentum from vortex light to itinerant electrons in quantum Hall graphene. In the latter, we demonstrated circular-polarization-dependent strong coupling in a 2D gas in the quantum Hall regime coupled to a microcavity. Our findings demonstrate the potential of chiral light to control light-matter interactions in quantum Hall systems. In the first part of this dissertation, we review our experimental demonstration of light-matter interaction beyond the dipole-approximation between electronic quantum Hall states and vortex light where the orbital angular momentum of light was transferred to electrons. Specifically, we identified a robust contribution to the radial photocurrent, in an annular graphene sample within the quantum Hall regime, that depends on the vorticity of light. This phenomenon can be interpreted as an optical pumping scheme, where the angular momentum of photons is transferred to electrons, generating a radial current, where the current direction is determined by the vorticity of the light. Our findings offer fundamental insights into the optical probing and manipulation of quantum coherence, with wide-ranging implications for advancing quantum coherent optoelectronics. In the second part of this dissertation, we review our experimental demonstration of a selective strong light-matter interaction by harnessing a 2D gas in the quantum Hall regime coupled to a microcavity. Specifically, we demonstrated circular-polarization dependence of the vacuum Rabi splitting, as a function of magnetic field and hole density. We provide a quantitative understanding of the phenomenon by modeling the coupling of optical transitions between Landau levels to the microcavity. This method introduces a control tool over the spin degree of freedom in polaritonic semiconductor systems, paving the way for new experimental possibilities in light-matter hybrids.Item ENGINEERING OPTICAL LATTICES FOR ULTRACOLD ATOMS WITH SPATIAL FEATURES AND PERIODICITY BELOW THE DIFFRACTION LIMIT and DUAL-SPECIES OPTICAL TWEEZER ARRAYS FOR RUBIDIUM AND YTTERBIUM FOR RYDBERG-INTERACTION-MEDIATED QUANTUM SIMULATIONS(2024) Subhankar, Sarthak; Rolston, Steven; Porto, Trey; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation is based on two independent projects and is therefore divided into two parts. The first half of this dissertation summarizes a series of investigations, both experimental and theoretical, that culminates in the realization of an optical lattice with a subwavelength spacing of $\lambda/4$, where $\lambda$ is the wavelength of light used to create the lattice. The second half of this thesis presents details on the design andconstruction of an apparatus for dual-species optical tweezer arrays of Rb and Yb for Rydberg-interaction-mediated quantum computation and simulation. Ultracold atoms trapped in optical lattices have proven to be a versatile, highly controllable, and pristine platform for studying quantum many-body physics. However, the characteristic single-particle energy scale in these systems is set by the recoil energy $E_R=h^2 /\left(8 m d^2\right)$. Here, $m$ is the mass of the atom, and $d$, the spatial period of the optical lattice, is limited by diffraction to ${\lambda}/{2}$, where $\lambda$ is the wavelength of light used to create the optical lattice. Although the temperatures in these systems can be exceedingly low, the energy scales relevant for investigating many-body physics phenomena, such as superexchange or magnetic dipole interactions, can be lower yet. This limitation can be overcome by raising the relevant energy scales of the system ($E_R^{\mathrm{eff}}=h^2 /\left(8 m d_{\mathrm{eff}}^2\right)$) by engineering optical lattices with spatial periodicities below the diffraction limit ($d_{\mathrm{eff}} < \lambda/2$). To realize this subwavelength-spaced lattice, we first generated a Kronig-Penney-like optical lattice using the nonlinear optical response of three-level atoms in spatially varying dark states. This conservative Kronig-Penney-like optical potential has strongly subwavelength barriers that can be less than 10 nm ($\equiv\lambda/50$) wide and are spaced $\lambda/2$ apart, where $\lambda$ is the wavelength of light used to generate the optical lattice. Using the same nonlinear optical response, we developed a microscopy technique that allowed the probability density of atoms in optical lattices to be measured with a subwavelength resolution of $\lambda/50$. We theoretically investigated the feasibility of stroboscopically pulsing spatially shifted 1D Kronig-Penney-like optical lattices to create lattices with subwavelength spacings. We applied the lattice pulsing techniques developed in this theoretical investigation to realize a $\lambda/4$-spaced optical lattice. We used the subwavelength resolution microscopy technique to confirm the existence of this $\lambda/4$-spaced optical lattice by measuring the probability density of the atoms in the ground band of the $\lambda/4$-spaced optical lattice. Single neutral atoms trapped in optical tweezer arrays with Rydberg interaction-mediated entangling gate operations have recently emerged as a promising platform for quantum computation and quantum simulation. These systems were first realized using atoms of a single species, with alkali atoms being the first to be trapped in optical tweezers, followed by alkaline-earth (like) atoms, and magnetic lanthanides. Recently, dual-species (alkali-alkali) optical tweezer arrays were also realized. Dual-species Rydberg arrays are a promising candidate for large-scale quantum computation due to their capability for multi-qubit gate operations and crosstalk-free measurements for mid-circuit readouts. However, a dual-species optical tweezer array of an alkali atom and an alkaline-earth (like) atom, which combines the beneficial properties of both types of atoms, has yet to be realized. In this half of the thesis, I present details on the design and construction of an apparatus for dual-species Rydberg tweezer arrays of Rb (alkali) and Yb (alkaline-earth like).Item Optimal Point-Spread-Function Engineering with Dynamic Optics and Event Cameras(2024) Shah, Sachin; Metzler, Christopher A; Computer Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Computational imaging systems co-design optics and algorithms to observe phenomena beyond the reach of traditional cameras. Point-spread-function (PSF) engineering is a powerful technique wherein a custom phase mask is integrated into an optical system to encode additional information into captured images. Used in combination with deep learning, such systems now offer state-of-the-art performance at three-dimensional molecule localization, extended depth-of-field imaging, lensless imaging, and other tasks. Recent hardware breakthroughs are unlocking unprecedented ultrafast capabilities such as micro-electromechanical system based spatial light modulators will allow us to module light at kilohertz rates and neuromorphic event cameras will enable kilohertz lower-power and high-dynamic-range capture. Unfortunately, existing theories and algorithms are unable to fully harness these new capabilities. This work answers a natural question: Can one encode additional information and achieve superior performance by leveraging the ultrafast capabilities of spatial light modulators and event cameras. We first prove that the set of PSFs described by static phase masks is non-convex and that, as a result, time-averaged PSFs generated by dynamic phase masks displayed on a spatial light modulator are fundamentally more expressive. We then derive the theoretical limits on three-dimensional tracking with PSF-engineered event cameras. Using these bounds, we design new optimal phase masks and binary amplitude masks. We demonstrate the efficacy of our designs through extensive simulations and validate our method with a simple lab prototype.Item HIGH PERFORMANCE NANOPHOTONIC CAVITIES AND INTERCONNECTS FOR OPTICAL PARAMETRIC OSCILLATORS AND QUANTUM EMITTERS(2024) Perez, Edgar; Srinivasan, Kartik; Hafezi, Mohammad; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Integrated photonic devices like photonic crystals, microring resonators, and quantum emitters produce useful states of light, like solitons or single photons, through carefully engineered light-matter interactions. However, practical devices demand advanced integration techniques to meet the needs of cutting-edge technologies. High performance nanophotonic cavities and interconnects present opportunities to solve outstanding issues in the integration of nanophotonic devices. In this dissertation I develop three core tools required for the comprehensive integration of quantum emitters: wavelength-flexible excitation sources with sufficient pump power to drive down stream systems, photonic interconnects to spatially link the excitation sources to emitters, and cavities that can Purcell enhance quantum emitters without sacrificing other performance metrics. To create wavelength-flexible excitation sources, a high-performance χ(3)microring Optical Parametric Oscillator (OPO) is realized in silicon nitride. Microring OPOs are nonlinear frequency conversion devices that can extend the range of a high-quality on-chip (or off-chip) laser source to new wavelengths. However, parasitic effects normally limit the output power and conversion efficiency of χ(3)microring OPOs. This issue is resolved by using a microring geometry with strongly normal dispersion to suppress parasitic processes and multiple spatial mode families to satisfy the phase and frequency matching conditions. Our OPO achieves world-class performance with a conversion efficiency of up to 29% and an on-chip output power of over 18 mW. To create photonic interconnects, Direct Laser Writing (DLW) is used to fabricate 3-dimensional (3D) nanophotonic devices that can couple light into and out of photonic chips. In particular, polymer microlenses of 20 μm diameter are fabricated on the facet of photonic chips that increase the tolerance of the chips to misaligned input fibers by a factor of approximately 4. To do so, we develop the on-axis DLW method for photonic chips, which avoids the so-called "shadowing" effect and uses barcodes for automated alignment with machine vision. DLW is also used to fabricate Polymer Nanowires (PNWs) with diameters smaller than 1 μm that can directly couple photons from quantum emitters into Gaussian-like optical modes. Comparing the same quantum emitter system before and after the fabrication of a PNW, a (3 ± 0.7)× increase in the fiber-coupled collection efficiency is measured in the system with the PNW. To refine the design of quantum emitter cavities, a toy model is used to understand the underlying mechanisms that shape the emission profiles of Circular Bragg Gratings (CBGs). Insights from the toy model are used to guide the Bayesian optimization of high-performance CBG cavities suitable for coupling to single-mode fibers. I also demonstrate cavity designs with quality factors (Q) greater than 100000, which can be used in future experiments in cavity quantum electrodynamics or nonlinear optics. Finally, I show that these cavities can be optimized for extraction to a cladded PNW while producing a Purcell enhancement factor of 100 with efficient extraction into the fundamental PNW mode. The tools developed in this dissertation can be used to integrate individual quantum emitter systems or to build more complex systems, like quantum networks, that require the integration of multiple quantum emitters with multiple photonic devices.Item TUNABLE ATOMIC LINE MONOCHROMATORS FOR BRILLOUIN SPECTROSCOPY(2024) Hutchins, Romanus Joshua; Scarcelli, Giuliano; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Brillouin microscopy, a non-contact, spatially-resolved imaging method, provides insights into the mechanical information of samples. The first generation of Brillouin microscopes combined confocal microscopes and etalon-based spectrometers. In this setup, a confocal microscope scans a laser across the sample pixel-by-pixel, while the etalon spectrometer measures the Brillouin shift frequency at each pixel. Despite the extended image acquisition times in biological samples (>20 ms/pixel), advancements have been made in the field to enhance the overall speed of Brillouin imaging. For example, line-scan Brillouin spectrometers use orthogonal detection to measure the Brillouin scattering at a row of pixels in a single shot. The pixel multiplexing in one-dimension (1D) improved the Brillouin imaging speeds 20-fold. Further multiplexing to two dimensions, or full-field spectroscopy, where the frequency domain is sequentially acquired but all the pixels in the field of view are simultaneously measured at each frequency, can further improve the average image acquisition time. However, there are currently no solutions for sub-picometer (sub-GHz) spectral resolution, two-dimensional (2D) multiplexing of Brillouin images. Here, I use the laser induced circular dichroism (LICD) effect in atomic vapors to create monochromators for 2D multiplexing at high spectral resolutions. These atomic line monochromators possess spectral resolutions dependent on the linewidth of the atomic resonance (~MHz), and they are ideal for pixel multiplexing because they have spectral analysis capabilities that do not depend on the spatial separation of spectral components. First, I present a full characterization of a tunable atomic line monochromator. I measure the transmission, spectral resolution, and spectral tunability of the device, as well as demonstrate whole-image transmission through the atomic line monochromator. Next, for practical implementations of the device to Brillouin spectroscopy, I created an atomic line monochromator based on a ladder-type atomic transition. This iteration of the device suffers from less noise than the previous version, leading to the first Brillouin measurements with this device. Finally, I present the first full-field Brillouin microscope by demonstrating whole Brillouin imaging with orthogonal detection with an atomic line monochromator.Item Nonlinear and Stochastic Dynamics of Optoelectronic Oscillators(2024) Ha, Meenwook; Chembo, Yanne K.; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Optoelectronic oscillators (OEOs) are nonlinear, time-delayed and self-sustained microwave photonic systems capable of generating ultrapure radiofrequency (RF) signals with extensive frequency tunabilities. Their hybrid architectures, comprising both optical and electronic paths, underscore their merits. One of the most notable points of OEOs can be unprecedentedly high quality factors, achieved by storing optical energies for RF signal generations. Thanks to their low phase noise and broad frequency tunabilities, OEOs have found diverse applications including chaos cryptography, reservoir computing, radar communications, parametric oscillator, clock recovery, and frequency comb generation. This thesis pursues two primary objectives. Firstly, we delve into the nonlinear dynamics of various OEO configurations, elucidating their universal behaviors by deriving corresponding envelope equations. Secondly, we present a stochastic equation delineating the dynamics of phases and explore the intricacies of the phase dynamics. The outputs of OEOs are defined in their RF ports, with our primary focus directed towards understanding the dynamics of these RF signals. Regardless of their structural complexities, we employ a consistent framework to explore these dynamics, relying on the same underlying principles that determine the oscillation frequencies of OEOs. To comprehend behaviors of OEOs, we analyze the dynamics of a variety of OEOs. For simpler systems, we can utilize the dynamic equations of bandpass filters, whereas more complex physics are required for expressing microwave photonic filtering. Utilizing an envelope approach, which characterizes the dynamics of OEOs in terms of complex envelopes of their RF signals, has proven to be an effective method for studying them. Consequently, we derive envelope equations of these systems and research nonlinear behaviors through analyses such as investigating bifurcations, stability evaluations, and numerical simulations. Comparing the envelope equations of different models reveals similarities in their dynamic equations, suggesting that their dynamics can be governed by a generalized universal form. Thus, we introduce the universal equation, which we refer to as the universal microwave envelope equation and conduct analytical investigations to further understand its implications. While the deterministic universal equation offers a comprehensive tool for simultaneous exploration of various OEO dynamics, it falls short in describing the stochastic phase dynamics. Our secondary focus lies in investigating phase dynamics through the implementation of a stochastic approach, enabling us to optimize and comprehend phase noise performance effectively. We transform the deterministic universal envelope equation into a stochastic delay differential form, effectively describing the phase dynamics. In our analysis of the oscillators, we categorize noise sources into two types: additive noise contribution, due to random environmental and internal fluctuations, and multiplicative noise contribution, arising from noisy loop gains. The existence of the additive noise is independent of oscillation existence, while the multiplicative noise is intertwined with the noisy loop gains, nonlinearly mixing with signals above the threshold. Therefore, we investigate both sub- and above-threshold regimes separately, where the multiplicative noise can be characterized as white noise and colored noise in respective regimes. For the above-threshold regime, we present the stochastic phase equation and derive an equation for describing phase noise spectra. We conduct thorough investigations into this equation and validate our approaches through experimental verification. In the sub-threshold regime, we introduce frameworks to experimentally quantify the noise contributions discussed in the above-threshold part. Since no signal is present here and the oscillator is solely driven by the stochastic noise, it becomes feasible to reverse-engineer the noise powers using a Fourier transform formalism. Here, we introduce a stochastic expression written in terms of the real-valued RF signals, not the envelopes, and the transformation facilitates the expressions of additive and multiplicative noise contributions as functions of noisy RF output powers. The additive noise can be defined by deactivating the laser source or operating the intensity modulator at the minimum transmission point, given its independence from the loop gains. Conversely, the expression for the multiplicative noise indicates a dependence on the gain, however, experimental observations suggest that its magnitude may remain relatively constant beyond the threshold.