This thesis presents research on the initialization, control, and readout of electron spin states in gate defined GaAs quantum dots. The first three experiments were performed with Singlet-Triplet spin qubits in double quantum dots, while the remaining two experiments were performed with an Exchange-Only spin qubit in a triple quantum dot. / Physics

Two dimensional electronic materials provide a vibrant area for applying basic quantum mechanics and scattering theory. In quantum corrals, multiple scattering leads to resonances closely approximating eigenstates of an equivalently shaped billiard. We extend the analogy using methods from acoustics to demonstrate that the billiard conception of quantum corrals is a useful one even in wavelength regimes close to corral size. Resonance widths can be described by a simple relationship proportional to the perimeter to area ratio of the enclosure and the average reflection of a classical path. / Physics

Conventional CMOS (the current dominant technology for VLSI) implemented with ever smaller transistors is expected to encounter serious problems in the near future with the need for difficult fabrication technologies. The most important problem is heat generation. The desire for device density, power dissipation and performance improvement necessitates new technologies that will provide innovative solutions to integration and computations. Nanotechnology, especially Quantum-dot Cellular Automata (QCA) provides new possibilities for computing owing to its unique properties. Numerous nanoelectronic devices are being investigated and many experimental devices have been developed. Thus, high level circuit design is needed to keep pace with changing physical studies. The circuit design aspects of QCA have not been studied much because of its novelty. Arithmetic units, especially multipliers and dividers play an important role in the design of digital processors and application specific systems. Therefore, designs for parallel multipliers and dividers are presented using this technology. Optimal design of parallel multipliers for Quantum-Dot Cellular Automata is explored in this dissertation. As a main basic element to build multipliers, adders are implemented and compared their performances with previous adders. And two different layout schemes that single layer and multi-layer wire crossings are compared and analyzed. This dissertation proposes three kinds of multipliers. Wallace and Dadda parallel multipliers, quasi-modular multipliers, and array multipliers are designed and simulated with several different operand sizes. Also array multipliers that are well suited in QCA are constructed and formed by a regular lattice of identical functional units so that the structure is conformable to QCA technology without extra wire delay. All these designs are constructed using coplanar layouts and compared with other QCA multipliers. The delay, area and complexity are compared for several different operand sizes. This research also studies divider designs for quantum-dot cellular automata. A digit recurrence restoring binary divider is a conventional design that serves as a baseline. By using controlled full subtractor cell units, a relatively simple and efficient implementation is realized. The Goldschmidt divider using the new architecture (data tag method) to control the various elements of the divider is compared for the performance. / text

This thesis focuses on reducing the delay of non-restoring division. Although the digit recurrence division is lower in complexity and occupies a smaller area than division by convergence, it has a drawback: slow division speed. To mitigate this problem, two modification ideas are proposed here for the non-restoring division, the fastest division algorithm of the digit recurrence division methods. For the first proposed approach, the delay of the multiplexer for selecting the quotient digit and determining the way to calculate the partial remainder can be reduced through inverting the order of its flowchart. Second, one adder and one inverter can be removed by using a new quotient digit converter. To prove these ideas are valid, the simulation results comparing the modified non-restoring division and the standard non-restoring division are provided. / text

Semiconductor nanocrystals, otherwise known as Quantum dots (Q dots), are a new type of fluorophore that demonstrates many advantages over conventional organic fluorophores. These advantages offer the opportunity to improve known immunofluorescent methods and immunofluorescent biosensors for rapid and portable bacterial detection in water. The detection of the micro organism Escherichia coli O157:H7 by attenuation of a fluorophore’s signal in water was evaluated alone and in the presence of another bacterial species. A sandwich immunoassay with antibodies adhered to SU-8 as a conventional comparison to our novel attenuation detection was also conducted. The assays were tested for concentration determination as well as investigation for cross reactivity and interference from other bacteria and from partial target cells. In order to immobilize the capture antibodies on SU-8, an existing immobilization self-assembly monolayer (SAM) for glass was modified. The SAM was composed of a silane ((3-Mercaptopropyl) trimethoxysilane (MTS)) and hetero-bifunctional cross linker (N-γ-maleimidobutyryloxy succinimide ester (GMBS)) was utilized in this procedure. The SU-8 surface was activated using various acids baths and oxygenated plasma, and it was determined that the oxygenated plasma yielded the best surface attachment of antibodies. The use of direct fluorophore signal attenuation for detection of the target E. coli resulted in the lowest detectable population of 1x10¹ cfu/mL. It was not specific enough for quantitative assessment of target concentration, but could accurately differentiate between targeted and non-targeted species. The sandwich immunofluorescent detection on SU-8 attained the lowest detectable population of 1x10⁴ cfu/ml. The presence of Klebsiella pneumoniae in solution caused some interference with detection either from cross reactivity or binding site blocking. Partial target cells also caused interference with the detection of the target species, mainly by blocking binding sites so that differences in concentration were not discernable. The signal attenuation not only had a better lowest detectable population but also had less measurement error than the sandwich immunoassay on SU-8 which suffered from non-uniformed surface coverage by the antibodies.

This dissertation presents novel applications of ligand-capped II-VI semiconductor nanocrystals (i.e. CdSe and CdTe).Hybrid polymer-nanocrystal thin films were prepared using a bottom-up electrochemical crosslinking method, where thiophene-functionalized CdSe NCs were wired to electron-rich 3,4-dioxy-substituded thiophene polymers. Both nanocomposite and effective monolayer (EML) films were achieved by controlling monomer feed ratios during the crosslinking steps. These hybrid thin films showed enhanced photoelectrochemical current efficiencies with a variety of solution acceptor molecules compared to polymer control films, which was due to sensitization by the CdSe NCs. The electronic structure of the polymer played a critical role in the potential (doping) dependent hole capture efficiency from photoexcited CdSe NCs. Furthermore, photocurrent efficiencies were correlated with nanocrystal size, which was a direct product of frontier orbital energy shifting due to quantum confinement effects.All-inorganic CdTe-CdSe nanocrystal solar cells were fabricated by a facile layer-by-layer procedure. A low-temperature sintering strategy was utilized to electronically couple the nanocrystal thin films, which maintained the individual electronic properties of the nanocrystals. The electrical characteristics of these solar cells displayed predictable trends in open circuit voltage with varying CdSe NC diameter.Novel CdSe NC diffraction gratings were prepared by a facile microcontact molding procedure. These transmission gratings showed exceptionally high diffraction efficiencies that were dependent on optimum grating morphologies and the refractive index contrast provided by the nanocrystals, which was size-dependent. These films also showed promise as coupling gratings for internal reflection elements.

In this work, the Dyson's equation formalism is outlined and applied toseveral open quantum systems. These systems are composed of a core,quantum-mechanical set of discrete states and several continua, representing macroscopic systems. The macroscopic systems introducedecoherence, as well as allowing the total particlenumber in the system to change.Dyson's equation, an expansion in terms of proper self-energy terms, isderived. The hybridization of two quantum levelsis reproduced in this formalism, and it is shown that decoherence followsnaturally when one of the levels is replaced by a continuum.The work considers three physical systems in detail. The first,quantum dots coupled in series with two leads, is presented in a realistic two-level model. Dyson's equation is used to account for the leads exactly to all ordersin perturbation theory, and the time dynamics of a single electron in the dotsis calculated. It is shown that decoherence from the leads damps the coherentRabi oscillations of the electron. Several regimes of physical interest areconsidered, and it is shown that the difference in couplings of the two leadsplays a central role in the decoherence processes.The second system relates to the decay-out ofsuperdeformed nuclei. In this case, decoherence is provided by coupling to theelectromagnetic field. Two, three, and infinite-level models are consideredwithin the discrete system. It is shown that the two-level model is usuallysufficient to describe decay-out for the classic regions of nuclearsuperdeformation. Furthermore, a statistical model for the normal-deformedstates allows extraction of parameters of interest to nuclear structure fromthe two-level model. An explanation for the universality of decayprofiles is also given in that model.The final system is a proposed small molecular transistor. TheQuantum Interference Effect Transistor is based on a single monocyclic aromatic annulene molecule, with twoleads arranged in the meta configuration. This device is shown to be completely opaque to charge carriers, due to destructive interference. Thiscoherence effect can be tunably broken by introducing new paths with a real orimaginary self-energy, and an excellentmolecular transistor is the result.

Prostate cancer is one of the leading causes of death by cancer for men. Focal therapy is being tested to target only the dominant cancer lesion in the prostate. However, due to the need to ensure that the laser is targeting only the cancer, a real-time treatment monitoring system is required. A combined optical-ultrasound monitoring system is in development at Princess Margaret Hospital based on different optical properties for coagulated versus normal tissue. In this project, we developed a light delivery and collection device that is compatible for use with an existing trans-rectal ultrasound-imaging probe. Computer-aided design software was used to visualize the prototype in relation to the trans-rectal ultrasound probe. This thesis describes the critical tasks necessary to assemble the final prototype, including listing of specifications, selection of device material based on safety and mechanical properties, method of prototype fabrication, positioning and fixation of optical fibers and testing.

Prostate cancer is one of the leading causes of death by cancer for men. Focal therapy is being tested to target only the dominant cancer lesion in the prostate. However, due to the need to ensure that the laser is targeting only the cancer, a real-time treatment monitoring system is required. A combined optical-ultrasound monitoring system is in development at Princess Margaret Hospital based on different optical properties for coagulated versus normal tissue. In this project, we developed a light delivery and collection device that is compatible for use with an existing trans-rectal ultrasound-imaging probe. Computer-aided design software was used to visualize the prototype in relation to the trans-rectal ultrasound probe. This thesis describes the critical tasks necessary to assemble the final prototype, including listing of specifications, selection of device material based on safety and mechanical properties, method of prototype fabrication, positioning and fixation of optical fibers and testing.

Currently, a major challenge for solid-state spin qubit systems is achieving one-qubit operations on a timescale shorter than the spin coherence time, T2*, a goal currently two orders of magnitude away. By taking advantage of the quasi-one-dimensional structure of a nanowire and the strong spin-orbit interaction of InAs, it is estimated that π-rotations can be implemented using electric dipole spin resonance on the order of 10 ns. To this end, a procedure for the fabrication of homogeneous InAs nanowire quantum dot devices is presented herein for future investigations of solid state spin qubits as a test bed for quantum computing. Both single and double quantum dot systems are formed using local gating of InAs nanowires. Single quantum dot systems were characterized through electron transport measurements in a dilution refrigerator; in one case, the charging energy was measured to be 5.0 meV and the orbital energy was measured to be 1.5-3.5 meV. The total capacitance of the single quantum dot system was determined to be approximately 30 aF. An estimate of the quantum dot geometry resulting from confinement suggests that the quantum dot is approximately 115 nm long. The coupling energy of the double quantum dot system was measured to be approximately 4.5 meV. The electron temperature achieved with our circuitry in the dilution refrigerator is estimated to be approximately 125 mK.