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
3 results
Search Results
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 ACTUATION OF MULTIFUNCTIONAL HARD NANOPARTICLES FOR ACTIVELY CONTROLLED DRUG RELEASE(2019) Sangtani, Ajmeeta; Delehanty, James B; Stroka, Kimberly M; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Systemic drug delivery relies on repeated dosing of large concentrations of poorly targeted drug leading to off-target toxicity. Recently, nanoparticle (NP)-mediated drug delivery (NMDD) has been developed as an approach to overcome the limitations of traditional drug delivery. The unique size-dependent properties of NPs and their ability to augment the activity of attached/loaded cargos makes them attractive drug delivery vectors. NPs are classified into two categories (soft or hard depending on their material composition) and our understanding of how to load and control soft NP materials currently surpasses that of hard NPs. In this dissertation we seek to further our fundamental knowledge of hard NP-based drug delivery systems. In Aim 1 we utilize a quantum dot (QD)-cell uptake peptide complex as a central scaffold to append various responsive peptide-drug constructs in order to modulate the toxicity of one of the most widely used chemotherapeutics, doxorubicin. By doing a comparative study of four chemical linkages, we determine the role played by attachment chemistry in controlling drug release. In Aim 2, we utilize the knowledge gained from Aim 1 to develop a system capable of overcoming multidrug resistance in cancer cells, which is known to severely limit the efficacy of chemotherapeutics. Our hard NP conjugate system is unique as it is one of the few systems reported in the literature to bypass multidrug resistance pumps without the need for exogenous drugs. Finally, in Aim 3 we append a peptide for membrane targeting and a photosensitizing drug capable of generating reactive oxygen species to the QD. This multifunctional system displays augmented therapeutic efficacy of the appended photosensitizer by delivering it to the membrane of cells and controlling its actuation using energy transfer. The work described here details basic concepts for the design of “smart” hard NP materials for internally and externally-triggered, active release of surface-appended drug cargos. Additionally, we hope to elucidate the important design considerations that must be taken into account when designing hard NP systems for controlled drug delivery.Item Optical nonlinearities near single photon level with a quantum dot coupled to a photonic crystal cavity(2011) Sridharan, Deepak; Waks, Edo; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Over the last decade, exponential increase of information bandwidth over the internet and other communication media has increased the total power consumed by the devices associated with information exchange. With ever increasing number of users, and packing of a higher number of devices onto a chip, there is a great need for reduction in not only the power consumption of the devices but also the costs associated with information transfer. Currently, the benchmark in the energy consumption per logic operation is at femtojoule level and is set by the CMOS industry. However, optical devices based on single photon emitters coupled to a microcavity have the potential to reduce the optical power dissipation down to attojoule levels wherein only few 10s of photons are consumed for a logic operation. This work presents our theoretical and experimental efforts towards realization of all optical device based on the enhanced nonlinearities of a single photon emitter in a photonic crystal cavity. We show that a single quantum dot coupled to a photonic crystal cavity can be used to route an incoming optical beam with optical power dissipation of 14 attojoules, corresponding to only 65 photons. This value is well below the operational level for current CMOS devices indicating the potential for chip based optical transistors for reduction in energy consumption. The single photon emitters that we use to create the nonlinearity are the quantum dots, which are semiconductor nanostructures that exhibit a discrete energy spectrum. The interaction of the quantum dot, with light confined inside a photonic crystal cavity, results in strong atom-photon interactions which can be used for ultra-low power all optical switching. The strong interactions between a quantum dot and photonic crystal cavity can be further utilized to realize quantum computation schemes on a chip. I also describe techniques for integrating this transistor into an optical circuit, and discuss methods for post fabrication tuning to make reconfigurable active photonic devices that implement optical data processing at low light levels.