Physics
Permanent URI for this communityhttp://hdl.handle.net/1903/2269
Browse
50 results
Search Results
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 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 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 Spatiotemporal Optical Vortices(2023) Hancock, Scott; Milchberg, Howard; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Light beams carrying orbital angular momentum (OAM) have become a mainstay of optical science and technology. In these beams, well-known examples of which are the Laguerre-Gaussian (LG_pm ) and Bessel-Gaussian (BG_m ) beams, the OAM vector points parallel or anti-parallel to propagation, and is associated with a phase winding 2πm in the plane transverse to the propagation direction, where integer m is the winding order or the “topological charge”. Such beams can be monochromatic.Recently, our group discovered a new type of OAM structure that naturally emerges from nonlinear self-focusing, which we dubbed the spatio-temporal optical vortex (STOV). Here, the phase winding exists in a spatiotemporal plane, with the OAM pointing transverse to propagation. In this dissertation, we extend the generation of STOV-carrying pulses to the linear regime, demonstrating their generation using a 4f pulse shaper and measuring their free-space propagation using a new ultrafast single-shot space- and time-resolving diagnostic, TG-SSSI (transient-grating single-shot supercontinuum spectral interferometry). We then demonstrate that transverse OAM is a property of photons by experimentally confirming the conservation of transverse OAM in second harmonic generation. Because the field of STOVs is so new, a first principles theory for their transverse OAM was lacking. We developed such a theory for transverse OAM that predicts half integer values of OAM and the existence of a STOV polariton in dispersive media. The surprise of half-integer OAM values launched a debate in the OAM community, which has been resolved in favor of our theory by our most recent experiments. These explore how phase and amplitude perturbations can impart spatiotemporal torques to light. We find that transverse OAM can be imparted to light pulses only for (1) sufficiently fast transient phase perturbations or (2) energy removal from a pulse already possessing transverse OAM.Item Mid-Infrared Laser Driven Avalanche Ionization and Low Frequency Radiation Generation(2022) Schwartz, Robert Max; Milchberg, Howard; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In this dissertation, we discuss the applications of intense mid-infrared laser interactions in three main topics. First, we demonstrate and discuss the remote detection of radioactive materials using avalanche breakdowns driven by picosecond, mid-infrared laser pulses. In the presence of radioactive materials, an enhanced population of free electrons and weakly bound ions are created in air. Laser driven avalanche ionization is a powerful tool for amplifying and detecting this weak signature, allowing for detection at standoff distances beyond the stopping distance of the radioactive particles. This technique can be applied more generally to the detection of any low density plasma. In the second section, we apply a similar method to measure laser ionization yields in atmospheric pressure gas across an extremely wide range. Finally, we demonstrate and discuss the generation of THz and low harmonics from two-color mid-infrared laser pulses. This technique allows for the generation of highly efficient, ultra-broadband coherent radiation.Item Experiments with Frequency Converted Photons from a Trapped Atomic Ion(2022) Hannegan, John Michael; Quraishi, Qudsia; Linke, Norbert; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Trapped atomic ions excel as local quantum information processing nodes, given their long qubit coherence times combined with high fidelity single-qubit and multi-qubit gate operations. Trapped ion systems also readily emit photons as flying qubits, making efforts towards construction of large-scale and long-distance trapped-ion-based quantum networks very appealing. Two-node trapped-ion quantum networks have demonstrated a desirable combination of high-rate and high-fidelity remote entanglement generation, but these networks have been limited to only a few meters in length. This limitation is primarily due to large fiber-optic propagation losses experienced by the ultraviolet and visible photons typically emitted by trapped ions. These wavelengths are also incompatible with existing telecommunications technology and infrastructure, as well as being incompatible with many other emerging quantum technologies designed for useful tasks such as single photon storage, measurement, and routing, limiting the scalability of ion-based networks. In this thesis, I discuss a series of experiments where we introduce quantum frequency conversion to convert single photons at 493 nm, produced by and entangled with a single trapped $^{138}$Ba$^+$ ion, to near infrared wavelengths for reduced network transmission losses and improved quantum networking capabilities. This work is the first-ever to frequency convert Ba$^+$ photons, being one of three nearly concurrent demonstrations of frequency converted photons from any trapped ion. After discussing our experimental techniques and laboratory setup, I first showcase our quantum frequency converters that convert ion-produced single photons to both 780 nm and 1534 nm for improved quantum networking range, whilst preserving the photons' quantum properties. Following this, I present two hybrid quantum networking experiments where we interact converted ion-photons near 780 nm with neutral $^{87}$Rb systems. In the initial experiment, we observe, for the first time, interactions between converted ion-photons and neutral Rb vapor via slow light. The following experiment is a multi-laboratory project where we observe Hong-Ou-Mandel interference between converted ion-photons and photons produced by an ensemble of neutral Rb atoms, where notably these sources are located in different buildings and are connected and synchronized via optical fiber. Finally, I describe an experiment in which we verify entanglement between a $^{138}$Ba$^+$ ion and converted photons near 780 nm. These results are critical steps towards producing remote entanglement between trapped ion and neutral atom quantum networking nodes. Motivated by these experimental results, I conclude by presenting a theoretical hybrid-networking architecture where neutral-atomic based nondestructive single photon measurement and storage can be integrated into a long-distance trapped-ion based quantum network to potentially improve remote entanglement rates.Item Spatiotemporal Nonlinear Optical Effects in Multimode Fibers(2022) Dacha, Sai Kanth; Murphy, Thomas E; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The advent of the optical fiber in the second half of the 20th century has had numerous consequences not only for the advancement of telecommunication and information transfer technologies, but also for humanity as a whole. At the time of writing of this thesis, we live in a world that is defined by unprecedented and unparalleled access to information made possible by fiber optic cables that line the ocean beds. As the world becomes increasingly reliant upon the internet, the demand for access is outgrowing the pace at which the capacity of our fiber optic networks can be scaled up. In the past decade, a consensus has emerged among researchers in academia and the industry that we are now approaching the fundamental classical capacity limit of a conventional single mode fiber, namely the Shannon limit. This has spurred interest in multimode fibers that allow for hundreds of spatial modes to co-propagate, potentially allowing for at least an order of magnitude increase in capacity per fiber. While multiplexing in the spatial domain has the potential to offer significantly higher capacities, linear and nonlinear mixing between the spatial modes of a fiber are expected to play an important role in determining the capacity and performance of spatially multiplexed telecommunication systems. So far, multimode fibers have mostly been relegated to low-power short- distance links, as a result of which nonlinear propagation effects in the presence of multiple spatial modes has received relatively little attention. This thesis adds to a growing body of literature that is increasingly interested in uncovering the physics of multimodal propagation in the nonlinear regime. Although the need for spatial multiplexing is important factor driving research interest in this topic, experiments in recent years have revealed a plethora of complex spatiotemporal non- linear phenomena occurring in multimode fibers, including Kerr-induced beam self-cleaning, parametric instability processes and the existence of multimode solitons. This has sparked great interest in understanding multimodal nonlinearity from a fundamental and applied physics per- spective. Nonlinear multimode fiber optics is also of central importance for the development of high power fiber-coupled lasers as the larger core size of multimode fibers allow for far higher power throughput than current state-of-the-art lasers based on single mode fibers. Most literature reported thus far in multimodal nonlinear optics focuses on complex phe- nomena occurring when hundreds of spatial modes co-propagate in the nonlinear regime. While that has proven to be a fascinating field of study, there have not been many studies on experimental investigation of intermodal nonlinear effects in the presence of a small number of spatial modes. Furthermore, nonlinear phenomena in multimode fibers are ‘spatiotemporal’ in nature, meaning that the spatial and time-domain waveforms are intertwined, and the two degrees of freedom cannot be separated. Conventional measurement techniques are not capable of resolving such a multimodal beam in space and time simultaneously. Finally, most research involving nonlinear optical effects has thus far focused on linearly polarized modes in conventional fibers, and nonlinear effects involving vector orbital angular momentum modes remains relatively understudied. In this thesis, we seek to study nonlinear optical effects involving a small number of selectively excited scalar as well as vector spatial modes, and to develop experimental techniques capable of resolving the output in both space, frequency and time. To this end, we design, prototype and fabricate devices and methods aimed at exciting a small number of spatial modes of a fiber. In particular, we adopt methods from integrated photonics such as focused ion beam milling and metasurface devices to selectively excite modes of a fiber in an efficient manner. Spatial and temporal resolution of the output beam is achieved by the development of a new technique that involves raster-scanning of a near-field scanning optical microscopy probe, coupled with a high speed detector, along the output end-face of the fiber. Using these methods, we uncover and report our observations of spatiotemporal nonlinear phenomena that are unique to multimodal systems. We first demonstrate nonlinear intermodal interference of radially symmetric modes in step-index and parabolic index fibers. We then apply the same spatiotemporal measurement technique to observe the Kerr-induced beam self-cleaning phenomenon in a parabolic index fiber. And finally, we discuss our discovery of a spin-orbit coupled generalization of the well-known nonlinear polarization rotation phenomenon.Item High Resolution Mapping of Intracellular Mechanical Properties during Key Stages of Cancer Progression(2022) Nikolic, Milos; Scarcelli, Giuliano; Tanner, Kandice; Biophysics (BIPH); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The mechanical phenotype of the living cell is critical for survival following deformations due to confinement and fluid flow. Furthermore, in recent years mechanical interaction between cells and the cellular environment has been implicated as one of the key regulators of cancer progression and malignant transformation. Due to the need to better understand the mechanical properties of invasive cells and how the mechanical phenotype plays a role in cancer progression, several microrheology techniques have been applied to study cell mechanics in a range of in vitro environments. However, many of these techniques have been limited either to studying cells in only one type of environment (e.g. 2D), with limited resolution, or with invasive probes. To begin to address this question, in this dissertation we aim to quantify the mechanical state of cells in a broader range of different contexts and geometries. To do this we use Brillouin microscopy, a non-contact, label free, non-invasive technique which enables us to probe the mechanical response of cells in a wide range of complex microenvironments. Here we introduce an improved Brillouin microscope with improved signal and acquisition speed which enables us to perform biological studies at the single cell level. Using the improved Brillouin microscopy, we find that individual cells can be softer as function of the invasive potential, but that cells are able to dynamically change their mechanical properties across many different contexts. We validate our results using complementary microrheology methods such as atomic force microscopy and broadband optical tweezer microrheology. We directly observe changes in cell mechanics in key processes relevant for metastatic migration, as well as a function of external and internal parameters like morphology, ECM properties, intracellular factors, and cell-cell cooperativity during multicellular tissue organization. These results support the paradigm that the mechanical state of a cell is a dynamic parameter that varies as a consequence of the microenvironmental and functional context, in addition to the observable changes in cell’s mechanical properties due to malignant transformation.