The two-dimensional electron system in strongly coupled GaAs/Al0.3Ga0.7As double quantum wells has been studied by Shubnikov-de Haas¡]SdH¡^measurements. The degenerate subbands of the double quantum wells are lift into two subbands with a symmetric or anti- symmetric z-direction wave function. We observed that the SdH oscillation due to the second subband of anti-symmetric wave function. The effective mass of the second subband is linearly dependent on the magnetic field range from 0.680 T to 1.964 T. The mass enhancement for the double-quantum-well with an equal well thickness is greater than that with an unequal one. This mass enhancement is attributed to the electron-electron interaction.

No description available.

<p>Liposomes are excellent chemotherapy drug delivery agents, on the cutting edge of cancer treatment technology. Since liposomes are already used to deploy cancer drugs in patients, imaging capacity would make them dual-purpose "theranostic" vesicles. Intermolecular double quantum coherence (iDQC) MRI is uniquely suited to this application, as its contrast does not require any additional chemicals. Adding contrast agents to liposomes can be time-consuming, add to toxicity, interfere with membrane function, or adversely affect drug loading. Furthermore, iDQC contrast measures diffusion and thus directly depends on membrane permeability and related properties. In this set of experiments, it has been shown that iDQC signal from intra-liposomal water can be distinguished from that of bulk water, and that the T2 dynamics of intra-liposomal water are predictable and dependent on the percent of water encapsulated. These techniques to distinguish between water molecules based on their current physical circumstances lead to many novel possibilities in MRI, as nearly all the signal in conventional MRI is from water protons. Based on the signal to noise ratio in the aforementioned iDQC experiments, we predict that iDQC contrast from liposomes will be visible in vivo, and propose to prove this in a murine model. By examining intra-liposomal water, iDQC can be used to improve chemotherapy delivery via real time monitoring of liposome location and drug release.</p> / Thesis

Esta tese baseia-se no estudo da dinâmica e conformação de polímeros no estado sólido utilizando-se técnicas modernas de RMN. Para o estudo quantitativo da dinâmica molecular lenta dos grupos laterais em uma série de poli (alqui1 metacrilato)s que apresentam diferentes tamanhos para os seus grupos laterais foram utilizadas duas novas técnicas de exchange: centerband-only detection of exchange (CODEX) e pure exchange (PUREX). Rotações dos grupos ésteres de 180&#176 flip) acopladas a movimentos de pequenos ângulos em torno da cadeia principal (&#60 20&#176), que são associados a relaxação &#946 nestes polímeros, são observados distintamente. As porcentagens de grupos laterais que realizam os movimentos de flip foram obtidas com 3% de precisão. Esses valores decrescem com o tamanho do grupo lateral, indo de 34% (PMMA) até cerca de 10% (PcHMA) à temperatura ambiente. No PMAA nenhum movimento lento dos grupos laterais é detectado. A fração de grupos laterais que realizam o flip se mantém constante com o aumento da temperatura para o PMMA até próximo da sua transição vítrea (Tg), enquanto que para o PEMA, o PiBMA e o PcHMA essa fração aumenta continuamente até próximo da Tg (de 31% para 80% para o PEMA). Movimentos independentes de pequena amplitude (&#60 5&#176) que cooperam para a acomodação dos grupos laterais durante o flip das cadeias vizinhas também foram verificados. O monitoramento do sinal atribuído ao grupo CH2 através da técnica CODEX confirma os resultados obtidos para o movimento da cadeia principal. Além disso, observa-se em alguns poli(acri1atos &#945-substituídos) que o tamanho dos grupos laterais a também têm influência na fração dos grupos ésteres que sofrem reorientação a 25&#176C . Para o estudo da conformação de polímeros foram implementados experimentos Double Quantum, que determinam ângulos de torção entre pares 13C-13C na cadeia polimérica. Foram realizados experimentos para dois polímeros, poli(óxido etileno) - (POE) e poli(eti1eno teraftalato) - (PET), enriquecidos em 13C com e sem desacoplamento homonuclear (13C-13C) em um espectrômetro Variam Inova 400. / This work is based on the study of dynamics and conformation of solid-state polymers, using NMR modern techniques. For the quantitative study of slow sidegroup dynamics in a series of poly(alkyl methacrylate)s and other of poly(&#945-substituted acrylate)s with varying sidegroup sizes two new 13C exchange techniques were used: centerband-only detection of exchange (CODEX) and pure exchange (PUREX). Flips and small-angle motions of the ester groups associated with the p-relaxation are observed distinctly, and the fraction of slowly flipping groups has been measured with 3% precision. A decreasing in these values occurs growing the sidegroup size. In PMMA, 34% of sidegroups flip, while the fraction is c.a. 10% in PcHMA around room temperature. In PMAA, no slow sidegroup flips are detected. In PMMA, the flipping fraction is temperature-independent between 25&#176C and 96&#176C, while in PEMA, PiBMA, and PcHMA it increases continuously between room temperature and Tg (from 31 to 80% for PEMA). Backbone CH2 CODEX data confirm the results obtained for the main chain movements. Flip-independent small amplitude motions (&#60 5&#176) are also observed. Besides, it is noticed that in some poly(&#945 -substituted acrylate)s the a sidegroup size has influence in the fraction of slowly flipping ester groups at 25&#176C. For the study of polymers conformation Double Quantum NMR experiments were used, for torsion angles determination between 13C-13C pairs through the polymer chain. Experiments for two standards 13C labeled samples: poly(ethy1ene oxide) - (PEO) and poly(ethy1ene teraftalate) - (PET) were performed, with and without homonuclear decoupling (13C-13C), in a Varian Inova 400 spectrometer.

Esta tese baseia-se no estudo da dinâmica e conformação de polímeros no estado sólido utilizando-se técnicas modernas de RMN. Para o estudo quantitativo da dinâmica molecular lenta dos grupos laterais em uma série de poli (alqui1 metacrilato)s que apresentam diferentes tamanhos para os seus grupos laterais foram utilizadas duas novas técnicas de exchange: centerband-only detection of exchange (CODEX) e pure exchange (PUREX). Rotações dos grupos ésteres de 180&#176 flip) acopladas a movimentos de pequenos ângulos em torno da cadeia principal (&#60 20&#176), que são associados a relaxação &#946 nestes polímeros, são observados distintamente. As porcentagens de grupos laterais que realizam os movimentos de flip foram obtidas com 3% de precisão. Esses valores decrescem com o tamanho do grupo lateral, indo de 34% (PMMA) até cerca de 10% (PcHMA) à temperatura ambiente. No PMAA nenhum movimento lento dos grupos laterais é detectado. A fração de grupos laterais que realizam o flip se mantém constante com o aumento da temperatura para o PMMA até próximo da sua transição vítrea (Tg), enquanto que para o PEMA, o PiBMA e o PcHMA essa fração aumenta continuamente até próximo da Tg (de 31% para 80% para o PEMA). Movimentos independentes de pequena amplitude (&#60 5&#176) que cooperam para a acomodação dos grupos laterais durante o flip das cadeias vizinhas também foram verificados. O monitoramento do sinal atribuído ao grupo CH2 através da técnica CODEX confirma os resultados obtidos para o movimento da cadeia principal. Além disso, observa-se em alguns poli(acri1atos &#945-substituídos) que o tamanho dos grupos laterais a também têm influência na fração dos grupos ésteres que sofrem reorientação a 25&#176C . Para o estudo da conformação de polímeros foram implementados experimentos Double Quantum, que determinam ângulos de torção entre pares 13C-13C na cadeia polimérica. Foram realizados experimentos para dois polímeros, poli(óxido etileno) - (POE) e poli(eti1eno teraftalato) - (PET), enriquecidos em 13C com e sem desacoplamento homonuclear (13C-13C) em um espectrômetro Variam Inova 400. / This work is based on the study of dynamics and conformation of solid-state polymers, using NMR modern techniques. For the quantitative study of slow sidegroup dynamics in a series of poly(alkyl methacrylate)s and other of poly(&#945-substituted acrylate)s with varying sidegroup sizes two new 13C exchange techniques were used: centerband-only detection of exchange (CODEX) and pure exchange (PUREX). Flips and small-angle motions of the ester groups associated with the p-relaxation are observed distinctly, and the fraction of slowly flipping groups has been measured with 3% precision. A decreasing in these values occurs growing the sidegroup size. In PMMA, 34% of sidegroups flip, while the fraction is c.a. 10% in PcHMA around room temperature. In PMAA, no slow sidegroup flips are detected. In PMMA, the flipping fraction is temperature-independent between 25&#176C and 96&#176C, while in PEMA, PiBMA, and PcHMA it increases continuously between room temperature and Tg (from 31 to 80% for PEMA). Backbone CH2 CODEX data confirm the results obtained for the main chain movements. Flip-independent small amplitude motions (&#60 5&#176) are also observed. Besides, it is noticed that in some poly(&#945 -substituted acrylate)s the a sidegroup size has influence in the fraction of slowly flipping ester groups at 25&#176C. For the study of polymers conformation Double Quantum NMR experiments were used, for torsion angles determination between 13C-13C pairs through the polymer chain. Experiments for two standards 13C labeled samples: poly(ethy1ene oxide) - (PEO) and poly(ethy1ene teraftalate) - (PET) were performed, with and without homonuclear decoupling (13C-13C), in a Varian Inova 400 spectrometer.

O uso das quasi-particulas de Majorana que emergem nas bordas de um supercondutor topológico é uma plataforma promisora para computação quântica. Novas propostas usam quantum dots (QDs) para detectar sinais de Majorana. Este método tem duas vantagens: 1) Os QDs são os melhores dispositivos para estudar a co-existência de Kondo e Majorana, a qual têm sido reportada recentemente em experimentos. 2) O controle experimental preciso sobre os quantum dots que temos hoje em dia oferece a oportunidade única para manipular quasi-partículas de Majoranas dentro de sistemas com vários dots. Esta ideia abriu novos caminhos para o desenho de arquiteturas quânticas, nos aproximando do objetivo de implementar um computador quântico topológico. O caso mais simples em que se é possível manipular tais quasi-partículas é num quantum dot duplo (DQD). Este modelo oferece várias possibilidades para mover os Majoranas, incluindo múltiplas configurações geométricas dos dots como acoplamentos simétricos, lineares e em junções T. Neste trabalho vamos apresentar uma análise teórica das transiç?s dos sinais de Majorana dentro do DQD em sistemas interagentes e não interagentes. Vamos ver que é possível controlar a localização dos modos zero de Majorana mediante o incremento nas voltagens de gate dos QDs. Também vamos explorar como esses sinais interagem com o efeito Kondo que emerge em superposição com o modo zero de Majorana. Principalmente, vamos a usar dois métodos neste projecto: 1) Usamos as equações de movimento no formalismo de funções de Green para obter expressões exatas para a densidade de estados em sistemas não interagentes. Vamos apresentar o método the eliminação de Gauss-Jordan com grafos, o qual permite resolver rapidamente o sistema linear emergente nas equações de movimento. 2) Em sistemas Coulomb interagentes usamos NRG, no qual poderemos observar a interação entre o Majorana e o efeito Kondo. Vamos testar ambos os métodos nos modelos de um double quantum dot e um QD acoplado com uma cadeia de Majorana, com o qual vamos reproduzir os resultados presentes na literatura. Finalmente, incluímos a maior contribuição deste trabalho, o estudo de um DQD acoplado a uma cadeia de Majorana. / Majorana zero modes (MZMs) emerging at the edges of topological superconducting wires are a promising platform for fault-tolerant quantum computation. Novel proposals use quantum dots (QDs) coupled to the end of these wires to detect Majorana signatures. This detection method provides the following advantages: 1) This device allows to study the prospective coexistence of Kondo-Majorana signatures, which have been recently reported in experiments. 2) Today\'s precise experimental control over QDs offers the unique possibility of manipulating MZMs inside multi-dot systems. This innovative idea has enlightened the design of scalable quantum architectures, bringing us closer to the implementation of a topological quantum computer. The simplest case where Majorana manipulation is possible is in a double quantum dot (DQD). This system offers several possibilities for manipulation of MZMs, including different geometric configurations of the dots, from symmetric and linear couplings to T-dot junctions. In this project, we perform a theoretical study of the transitions of the Majorana signature in these geometries in non-interacting and interacting regimes. By tuning the dot\'s gate voltages, we will show that it is possible to control the localization of the MZM inside both dots. We will also explore the interplay of these signatures with the Kondo effect, which emerges in non-interacting dots in superposition with the MZM. We adopt two methods in this project: 1) The Green equations of motion (EOM) allow us to obtain exact expressions for the density of states in coulomb-non-interacting systems. We present the Graph -Gauss-Jordan elimination process as a simple-graphical method to solve the emergent linear systems in the EOM. 2) We use Wilson\'s numerical renormalization group (NRG) in interacting systems, to study the combined Kondo-Majorana physics. We will test these methods, first in a double quantum dot (DQD) (chapter 3) and then in a QD-Majorana model (chapter 4), where we confirm the results of previous papers [1-3]. Finally, we include the main contribution of this thesis, the study of a DQD coupled to a Majorana chain (chapter 5).

High–resolution multidimensional proton-detected NMR was used to study the solvent-exposed regions of a seven-helical integral membrane proton pump proteorhodopsin (PR). Fully deuterated PR samples with protons reintroduced to solvent-accessible sites through back exchange were prepared and found to produce NMR spectra with acceptable proton resolution (~0.2 ppm). Novel three-dimensional proton-detected chemical shift correlation spectroscopy was used for the identification and resonance assignment of the solvent–exposed regions of PR. Though most of the observed residues were located at the membrane interface there were notable exceptions, particularly in helix G. This helix contains the Schiff base-forming Lys231 and many conserved polar residues in the extracellular half. Solvent accessibility of helix G supports the hypothesis that high mobility of the F-G loop could transiently expose a hydrophilic cavity in the extracellular half of PR, and implies that such a cavity may be part of the protein’s proton-conduction pathway. / Natural Sciences and Engineering Research Council, Ontario Ministry of Training, Colleges, and Universities, Canadian Foundation for Innovation, Ontario Ministry of Research and Innovation, University of Guelph

This thesis consists of two parts. In the first part, the properties of excess electrons in water clusters are studied via a hybrid quantum and classical mechanics method. The existence of the solvated electron in water was experimentally demonstrated long ago, and it is among the most interesting charged species. However, a satisfactory characterization of the water clusters has always been a challenge. In our simulation, we treat a region of the cluster nearest to the centroid of the excess electron distribution quantum mechanically, while the rest of the water molecules are treated classically. The binding energies of a localized excess electron are calculated in clusters with sizes ranging from 16 to 300. The density distributions of the excess electrons verify the existence of both surface localization mode and interior localization model. We studied the energetically favored localization modes depending on the sizes of the clusters and the transition point. In the second part, the energy spectra, spin configurations, and entanglement characteristics of a system of four electrons in lateral double quantum dots are investigated using exact diagonalization (EXD), as a function of interdot separation, applied magnetic field, and strength of interelectron repulsion. As a function of the magnetic field, the energy spectra exhibit a low-energy band consisting of a group of six states, with the number six being a consequence of the conservation of the total spin of the four electrons and the ensuing spin degeneracies. These six states appear to cross at a single value of the magnetic field, with the crossing point becoming sharper for larger interdot distances. As the strength of the Coulomb repulsion increases, the six states tend to become degenerate and a well defined energy gap separates them from the higher-in-energy excited states. The appearance of the low-energy band is a consequence of the formation of a Wigner supermolecule. Using the spin-resolved pair-correlation functions, one can map the EXD many-body wave functions onto the spin functions associated with the four localized electrons. The ability to determine associated spin functions enables investigations concerning entanglement properties of the system of four electrons.

Part I of this thesis is concerned with cavity optomechanical systems subject to periodic driving. We develop a Floquet approach to solve time-periodic quantum Langevin equations in the steady state, show that two-time correlation functions of system operators can be expanded in a Fourier series, and derive a generalized Wiener-Khinchin theorem that relates the Fourier transform of the autocorrelator to the noise spectrum. Weapply our framework to optomechanical systems driven with two tones. In a setting used to prepare mechanical resonators in quantum squeezed states, we nd and study the general solution in the rotating-wave approximation. In the following chapter, we show that our technique reveals an exact analytical solution of the explicitly time-periodic quantum Langevin equation describing the dual-tone backaction-evading measurement of a single mechanical oscillator quadrature due to Braginsky, Vorontsov, and Thorne [Science 209, 547 (1980)] beyond the commonly used rotating-wave approximation and show that our solution can be generalized to a wide class of systems, including to dissipatively or parametrically squeezed oscillators, as well as recent two-mode backaction-evading measurements. In Part II, we study nonreciprocal optomechanical systems with several optical and mechanical modes. We show that an optomechanical plaquette with two cavity modes coupled to two mechanical modes is a versatile system in which isolators, quantum-limited phase-preserving, and phase-sensitive directional ampliers for microwave signals can be realized. We discuss the noise added by such devices, and derive isolation bandwidth, gain bandwidth, and gain-bandwidth product, paving the way toward exible, integrated nonreciprocal microwave ampliers. Finally, we show that similar techniques can be exploited for current rectication in double quantum dots, thereby introducing fermionic reservoir engineering. We verify our prediction with a weak-coupling quantum master equation and the exact solution. Directionality is attained through the interference of coherent and dissipative coupling. The relative phase is tuned with an external magnetic eld, such that directionality can be reversed, as well as turned on and off dynamically.

Optical electroabsorption modulators (EAMs) that utilize quantum wells (QWs) are known to exhibit high modulation sensitivity, which is required for the analog optical fiber link application, compared to other types of optical modulators. QW-EAMs utilize the change of absorption coefficients that depends on the change of electric field across the QW for the optical intensity modulation. This dissertation focuses on the theoretical analysis of the optical properties of asymmetric double QWs (ADQWs) and the systematic optimization of modulation sensitivity in low-voltage EAMs that incorporate ADQWs. In this structure, the accurate calculation of excitons is especially important because the excitonic as well as the band-to-band optical transitions dominate the optical properties at the operating wavelength. The complex linear optical susceptibility was calculated within the density matrix approach in the quasi-equilibrium regime for the low excitation power and through a thorough treatment of line broadening. Transition strengths were calculated in the wavevector space, which effectively includes valence subband mixing with the warping of the subbands, excitonic mixing effects, and possible optical selection rules (e.g., light polarization, spin of excitons). The calculated transmission properties of the waveguide EAMs were almost identical to the experimental data at the device operating bias range. The mixing of excitons in ADQWs was analyzed in detail in momentum space, which was demonstrated to be very important in the process of structural optimization of ADQWs. The optimization of the structural parameters revealed that at an adequate barrier position and well width, the barrier thickness affects the modulation efficiency the most. Subsequently, in InGaAsP-based waveguide type QW-EAMs that operate at 1550 nm, the optimization of only one variable the thickness of the coupling barrier of the ADQWs shows 380 % enhancement in the modulation sensitivity at a much lower bias field (70->35 kV/cm) compared with that of single-QW structures. This enhancement is found to be caused by the strong mixing of the two exciton states originating in different subband pairs.