Theses and Dissertations from UMD
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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
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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 SPIN-PHOTON INTERFACE USING CHARGE TUNABLE QUANTUM DOTS(2021) Luo, Zhouchen; Waks, Edo; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The unconditional security of quantum networks and unparalleled acceleration of quantum algorithms enabled by “quantum computers” has motivated significant research across scientific communities. Among these different architectures to achieve such quantum information processing paradigms, a promising and straightforward proposal is the use of photons as flying qubits to transfer quantum information as well as local quantum memories to store and process quantum information. Toward this goal, it is very important to develop a type of quantum memory that can efficiently interface with photons while possessing good qubit properties, including a long coherence time and good scalability. To date, researchers have developed promising solid state quantum memory platforms, such as defects in diamond and other group IV compounds, rare earth ions hosted in various materials and self-assembled quantum dots. While each platform has its strengths and challenges, this thesis will focus on charge tunable InAs quantum dots grown inside a GaAs matrix that is doped into a PN junction. Though not long after the first demonstration of optically active self-assembled quantum dots, researchers have already developed the idea to sandwich them inside a PN junction to tune their charge status. The spin manipulation in the strong coupling regime has been mostly using these dots without PN junction doping, which has resulted in limited dot-cavity cooperativity and spin lifetime due to electron tunneling. In this thesis, I will first show the design, fabrication and characterization of several common photonic cavities, with their performance compared. Second I will show strong coupling between a negatively charged quantum dot and photonic crystal cavity, where the resonant cavity reflectivity is strongly dependent on the spin state. Third I will show that the electron spin lifetime (T1) can be significantly shortened by an off-resonant laser that reaches the device surface. While the exact reason for this undesired effect is not clear yet, we did observe the thickness of the electron tunnel barrier of the quantum dot wafer can result in distinct spin properties. I will present electron spin T1 characterization across several different quantum dot samples with different electron tunneling barrier thickness. Lastly, I will present coherent control of electron spin using picosecond laser pulse and sidebands of modulated continuous wave laser with limited spin rotation fidelity due to the off-resonant laser induced deterioration of the spin properties.Item Chiral Quantum Optics using Topological Photonics(2020) Barik, Sabaysachi; Waks, Edo EW; Hafezi, Mohammad MF; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Topological photonics has opened new avenues to designing photonic devices along with opening a plethora of applications. Recently, even though there have been many interesting studies in topological photonics in the classical domain, the quantum regime has remained largely unexplored. In this thesis, I will demonstrate a recently developed topological photonic crystal structure for interfacing a single quantum dot spin with a photon to realize light-matter interaction with topolog-ical photonic states. Developed on a thin slab of Gallium Arsenide(GaAs) mem- brane with electron beam lithography, such a device supports two robust counter- propagating edge states at the boundary of two distinct topological photonic crystals at near-IR wavelength. I will show the chiral coupling of circularly polarized lights emitted from a single Indium Arsenide(InAs) quantum dot under a strong magnetic field into these topological edge modes. Owing to the topological nature of these guided modes, I will demonstrate this photon routing to be robust against sharp corners along the waveguide. Additionally, taking it further into the cavity-QED regime, we will build a topological photonic crystal resonator. This new type of resonator will be based on valley-Hall topological physics and sustain two counter- propagating resonator modes. Thanks to the robustness of the topological edge modes to sharp bends, the newly formed resonators can take various shapes, the simplest one being a triangular optical resonator. We will study the chiral coupling of such resonator modes with a single quantum dot emission. Moreover, we will show an intensity enhancement of a single dot emission when it resonantly couples with a cavity mode. This new topological photonic crystal platform paves paths for fault-tolerant complex photonic circuits, secure quantum computation, and explor- ing unconventional quantum states of light and chiral spin networks.Item TOPOLOGICAL PHOTONICS AND EXPERIMENTAL TECHNIQUES IN QUANTUM OPTICS(2020) ORRE, VENKATA VIKRAM; Hafezi, Mohammad; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Topological photonics is the study of how the geometries and topologies of devices can be used to manipulate the behavior of photons. Many topological models exhibit edge states, a defining feature of these models, which travel around the perimeter of the lattice and are not affected by disorder. These edge states can help create scalable delay lines, quantum sources of light, and lasers all of which are robust against fabrication-induced disorder and bends in photonic structures. This research proposal is structured into two parts. In the first half of this thesis, we investigate a topological model and study some of its quantum applications. First, we realize the anomalous quantum Hall effect in a photonic platform using a 2D array of ring resonators with zero flux threading the lattice. The lattice implements a Haldane model by using the next-nearest couplings in lattice to simulate a nonzero local gauge flux while having a net flux of zero. The lattice hosts edge states, which are imaged through a CCD camera and show robustness against missing site-defects, 90 degree bends and fabrication-induced disorder. We also demonstrate a topological non-trivial to trivial phase transition by simply detuning the ring resonances. Next, we show degenerate photon pair creation in an anomalous quantum Hall device using a dual-pump spontaneous fourwave mixing process. The linear dispersion in the edge band results in an efficient phase matching and shows up as maximum counts in spectral correlations. The flatness of edge band also allows us to tune the bandwidth of the quantum source by changing the pump frequencies. Furthermore, we verify the indistinguishability of the photons using a Hong-Ou-Mandel (HOM) experiment. Finally, we simulate the transport of time-bin entangled photons in an integer quantum Hall device. The edges states preserve the temporal correlations and are robust against fabrication induced disorder. In contrast, the bulk states in the device exhibit localization, which is manifested in bunching/anti-bunching behavior. In the second part, we explore a few experimental quantum optics techniques developed as a part of investigating quantum transport in topological devices. We demonstrate two experimental techniques: 1. We use an EOM-based time-lens technique to resolve temporal correlations of time-bin entangled photons, which would have been otherwise inaccessible due to the limited temporal resolution of single photon detectors. Our time-lens also maps temporal correlations to spectral correlations and provides a way of manipulating frequency-bin entangled photons. 2. We show frequency-resolved interference of two and three photons distinguishable in time, which would not have interfered in a standard Hong-Ou-Mandel (HOM) setup. Our setup can be extended to implement temporal boson sampling using phase modulators. Furthermore, we demonstrate time-reversed HOM-like interference using time-bin entangled photon pairs and show that the spectral correlations are sensitive to phase between photons. Lastly, we demonstrate some miscellaneous experimental techniques, such as the design of the electronics used for time-lens, optimal spontaneous parametric down conversion parameters, measuring joint spectral intensity using a chirped bragg grating, and simultaneous measurement of Hong-Ou-Mandel interference for different frequencies.Item Photon Thermalization in Driven Open Quantum Systems(2018) Wang, Chiao-Hsuan; Taylor, Jacob M; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Light is a paradigmatic quantum field, with individual excitations---photons---that are the most accessible massless particles known. However, their lack of mass and extremely weak interactions mean that typically the thermal description of light is that of blackbody radiation. As the temperature of the light decreases, the overall number of photons approaches zero. Therefore, efforts for quantum optics and optical physics have mostly focused on driving systems far from equilibrium to populate sufficient numbers of photons. While lasers provide a severe example of a nonequilibrium problem, recent interests in the near-equilibrium physics of so-called photon gases, such as in Bose condensation of light or in attempts to make photonic quantum simulators, suggest one re-examine near-equilibrium cases. In this thesis, we consider peculiar driven open quantum system scenarios where near-equilibrium dynamics can lead to equilibration of photons with a finite number, following a thermal description closer to that of an ideal gas than to blackbody radiation. Specifically, we show how laser cooling of a well-isolated mechanical mode or atomic motion can provide an effective bath which enables control of both the chemical potential and temperature of the resulting grand canonical ensemble of photon. We then theoretically demonstrate that Bose condensation of photons can be realized by cooling an ensemble of two-level atoms inside a cavity. Finally, we find that the engineered chemical potential for light not only admits future applications in many-body quantum simulations, facilitates preparation of near-equilibrium photonic states, but also enables an analogous voltage bias for photonic circuit elements.Item QUANTUM NOISE IN OPTICAL PARAMETRIC AMPLIFIERS BASED ON A LOSSY NONLINEAR INTERFEROMETER(2009) Sylla, Pape Maguette; Goldhar, Julius; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Optical Parametric Amplifiers (OPA) have been of wide interest for the past decades due to their potential for low noise amplification and generation of squeezed light. However, the existing OPAs for fiber applications are based on Kerr effect and require from few centimeters to kilometers of fiber for significant gain. In this thesis, I review the principles of phase sensitive amplification and derive the expression for gain of a lossless Kerr medium based Nonlinear Mach-Zehnder Interferometer (NMZI OPA) using a classical physics model . Using quantum optics, I calculate the noise of a lossless Kerr medium based OPA and show that the noise figure can be close to zero. Since in real life a Kerr medium is lossy, using quantum electrodynamics, I derive equations for the evolution of a wave propagating in a lossy Kerr medium such as an optical fiber. I integrate these equations in order to obtain the parametric gain, the noise and the noise figure. I demonstrate that the noise figure has a simple expression as a function of loss coefficient and length of the Kerr medium and that the previously published results by a another research group are incorrect. I also develop a simple expression for the noise figure for high gain parametric amplifiers with distributed loss or gain. In order to enable construction of compact parametric amplifiers I consider using different nonlinear media, in particular a Saturable Absorber (SA) and a Semiconductor Optical Amplifier (SOA). Using published results on the noise from SOA I conclude that that such device would be prohibitively noisy. Therefore, I perform a detailed analysis of noise properties of a SA based parametric amplifier. Using a quantum mechanical model of an atomic 3 level system and the Heisenberg's equations, I analyze the evolution in time of a single mode coherent optical wave interacting with a saturable absorber. I solve the simultaneous differential equations and find the expression for the noise figure of the SA based NMZI OPA. The results show that noise figure is still undesirably high. The source of the noise is identified. A new approach for low noise parametric amplifier operating with short pulses is proposed.