<p> Despite the tremendous progress of quantum cryptography, efficient quantum communication over long distances (&ge; 1000km) remains an outstanding challenge due to fiber attenuation and operation errors accumulated over the entire communication distance. Quantum repeaters (QRs), as a promising approach, can overcome both photon loss and operation errors, and hence significantly speedup the communication rate. Depending on the methods used to correct loss and operation errors, all the proposed QR schemes can be classified into three categories (generations). First generation QRs use heralded entanglement generation for the correction of erasure errors and entanglement purification for the correction of operation errors. Second generation QRs use heralded entanglement generation for the correction of erasure errors and quantum error correction for the correction of operation errors. third-generation QRs use quantum error correction for the correction of both erasure and operation errors respectively. It is important to develop robust protocols for quantum repeaters, and systematically compare the performance of various QRs.</p><p> We investigate the use of efficient error correcting codes for third-generation QRs that make use of small encoding blocks to fault-tolerantly correct both loss and operation errors. Our schemes use quantum parity codes. quantum polynomial codes and quantum Reed-Solomon codes for encoding quantum information and use teleportation-based error correction to systematically correct erasure and operation errors in a fault-tolerant manner. We describe a way to optimize the resource requirements and system parameters for these QRs with the aim of generating a secure key. We perform a systematic comparison among these codes and identify the parameter regimes of operation errors where each code performs the best.</p><p> We then perform a systematic comparison of the three generations of QRs by evaluating the cost of both temporal and physical resources, and identify the optimized QR architecture for a given set of experimental parameters. Our work provides a roadmap for the experimental realization of highly efficient quantum networks over transcontinental distances.</p><p>

<p> Standard Quantum Mechanics, although successful in terms of calculating and predicting results, is inherently diffcult to understand and can suffer from misinterpretation. Entropic Dynamics is an epistemic approach to quantum mechanics based on logical inference. It incorporates the probabilities that naturally arise in situations in which there is missing information. It is the author's opinion that an advantage of this approach is that it provides a clearer mental image with which to picture quantum mechanics. This may provide an alternate means of presenting quantum mechanics to students. After a theory is presented to students, an instructor will then work through the paradigmatic examples that demonstrate the theory. In this thesis, we will be applying Entropic Dynamics to some of those paradigmatic examples. We begin by reviewing probability theory and Bayesian statistics as tools necessary for the development of Entropic Dynamics. We then review the topic of entropy, building from an early thermodynamic interpretation to the informational interpretation used here. The development of Entropic Dynamics involves describing a particle in terms of a probability density, and then following the time evolution of the probability density based on diffusion-like motion and the maximization of entropy. At this point, the review portion of the thesis is complete. </p><p> We then move on to applying Entropic Dynamics to several of the paradigmatic examples used to explain quantum mechanics. The rst of these is wave packet expansion. The second is interference, which is the basis behind many of the important phenomena in quantum mechanics. The third is the double slit experiment, which provides some interesting insight into the subject of interference. In particular, we look at the way in which minima can occur without a mechanism for destructive interference, since probabilities only add. The idea of probability flow is very apparent at this point in the discussion. The next example is that of the harmonic oscillator. This leads to an interesting insight concerning rotation and angular momentum as it corresponds to the flow of probability. The last example explored is that of entanglement. The discussion begins with a review of EPR, but then comes to the interesting conclusion that many of the problems inherent in the traditional approach to entanglement do not exist in Entropic Dynamics. The last topic covered in this thesis consists of some remarks concerning the state of education research as it pertains to quantum mechanics and the ways in which Entropic Dynamics might address them.</p><p>

<p> Technology has been integrated into the modern era and continues to influence society, culture, and the individual. The digital influence has left a split in its wake that affects intergenerational relationships, value constructs, self-development, and the aesthetics of attachment. The paradigm that dominates the majority of psychological theory and practice is functioning from metanarrative models that are being rejected by younger generations. Using a hermeneutic method, this thesis explores the inception and continuing radical emergence of the technological self. Winnicott&rsquo;s theory of transitional objects and potential space, along with Kaufman&rsquo;s quantum physics theory of radical emergence, are utilized to reveal how the Internet and digital devices function to fulfill the needs of Millennials and Generation Zers. Psychoanalysis is facing the demand to attend to the shifts and gaps between traditional, dominant therapy models and the millennial self that has become technologically embodied.</p><p>

<p> An interpretation of CMS searches for evidence of supersymmetry in the context of the minimal supersymmetric Standard Model (MSSM) is given. It is found that supersymmetric particles with color charge are excluded in the mass range below about 400 GeV, but neutral and weakly-charged sparticles remain non-excluded in all mass ranges. Discussion of the non-excluded regions of the model parameter space is given, including details on the strengths and weaknesses of existing searches, and recommendations for future analysis strategies. Advancements in the modeling of events arising from quantum chromodynamics and electroweak boson production, which are major backgrounds in searches for new physics at the LHC, are also presented. These methods have been implemented as components of CMS searches for supersymmetry in proton-proton collisions resulting in purely hadronic events (i.e., events with no identified leptons) at a center of momentum energy of 13 TeV. These searches, interpreted in the context of simplified models, exclude supersymmetric gluons (gluinos) up to masses of 1400 to 1600 GeV, depending on the model considered, and exclude scalar top quarks with masses up to about 800 GeV, assuming a massless lightest supersymmetric particle. A search for non-excluded supersymmetry models is also presented, which uses multivariate discriminants to isolate potential signal candidate events. The search achieves sensitivity to new physics models in background-dominated kinematic regions not typically considered by analyses, and rules out supersymmetry models that survived 7 and 8 TeV searches performed by CMS.</p>

Electronic band structure of various crystal orientations of relaxed and strained bulk, 1D and 2D confined semiconductors are investigated using nonlocal empirical pseudopotential method with spin-orbit interaction. For the bulk semiconductors, local and nonlocal pseudopotential parameters are obtained by fitting transport-relevant quantities, such as band gap, effective masses and deformation potentials, to available experimental data. A cubic-spline interpolation is used to extend local form factors to arbitrary q and the resulting transferable local pseudopotential V(q) with correct work function is used to investigate the 1D and 2D confined systems with supercell method. Quantum confinement, uniaxial and biaxial strain and crystal orientation effects of the band structure are investigated. Regarding the transport relavant quantities, we have found that the largest ballistic electron conductance occurs for compressively-strained large-diameter [001] wires while the smallest transport electron effective mass is found for larger-diameter [110] wires under tensile stress.

No description available.

<p>Studying the ultrafast dynamics of small molecules can serve as the first step in understanding the dynamics in larger chemically and biologically relevant molecules. To make direct comparisons with existing computational techniques, the photons used in pump-probe spectroscopy must make perturbative transitions between the electronic states of isolated small molecules. In this dissertation experimental investigations of ultrafast dynamics in electronic excitations of neutral ethylene and carbon dioxide are discussed. These experiments are performed using VUV/XUV femtosecond pulses as pump and probe. </p><p> To make photons with sufficient energy for single photon transitions, VUV and XUV light is generated by high harmonic generation (HHG) using a high pulse energy (&ap;30&ndash;40 mJ) Ti:sapphire femtosecond laser. Sufficient flux must be generated to enable splitting of the HHG light into pump and probe arms. The system produces >10¹⁰ photons per shot, corresponding to nearly 10 MW of peak power in the XUV. Using a high flux of high energy photons creates a unique set of challenges when designing a detector capable of performing pump-probe experiments. A velocity map imaging (VMI) detector has been designed to address these challenges, and has become a successful tool facilitating studies into molecular dynamics that were not possible before its implementation. </p><p> The emphasis on using high energy, single photon transitions allowed theoretical calculations to be directly compared to experimental yields for the first time. This comparison resolved a long standing issue in the excited state lifetime of ethylene, and provided a confirmation of the branching ratio between the two nonadiabatic relaxation pathways that return ethylene back to its ground state from the &pi;*. The participation of the 3s Rydberg state has also been measured by collecting the time resolved photoelectron spectrum during the dynamics on ethylene&rsquo;s &pi;* excited state, confirming calculations predicting the effect of the 3s. </p><p> In carbon dioxide the first time resolved measurement in the lowest electronic excitation of carbon dioxide has been performed. A high kinetic energy release channel shows the signature of wavepacket dynamics within the excited state manifold. Deviation from the direct dissociation predicted for the pumped state provides experimental evidence confirming theoretical predictions of nonadiabatic transitions within the lowest lying electronically excited states. </p>

<p> Engineered quantum systems are poised to revolutionize information science in the near future. A persistent challenge in applied quantum technology is creating controllable, quantum interactions while preventing information loss to the environment, decoherence. In this thesis, we realize mesoscopic superconducting circuits whose macroscopic collective degrees of freedom, such as voltages and currents, behave quantum mechanically. We couple these mesoscopic devices to microwave cavities forming a cavity quantum electrodynamics (QED) architecture comprised entirely of circuit elements. This application of cavity QED is dubbed Circuit QED and is an interdisciplinary field seated at the intersection of electrical engineering, superconductivity, quantum optics, and quantum information science. Two popular methods for taming active quantum systems in the presence of decoherence are discrete feedback conditioned on an ancillary system or quantum reservoir engineering. Quantum reservoir engineering maintains a desired subset of a Hilbert space through a combination of drives and designed entropy evacuation. Circuit QED provides a favorable platform for investigating quantum reservoir engineering proposals. A major advancement of this thesis is the development of a quantum reservoir engineering protocol which maintains the quantum state of a microwave cavity in the presence of decoherence. This thesis synthesizes strongly coupled, coherent devices whose solutions to its driven, dissipative Hamiltonian are predicted a <i>priori</i>. This work lays the foundation for future advancements in cavity centered quantum reservoir engineering protocols realizing hardware efficient circuit QED designs. </p>

<p> In this dissertation, we describe, characterize, and demonstrate the operation of a dual-in, dual-out, all-optical, fiber-based quantum switch. This "cross-bar" switch is particularly useful for applications in quantum information processing because of its low-loss, high-speed, low-noise, and quantum-state-retention properties. </p><p> Building upon on our lab's prior development of an ultrafast demultiplexer ^[1-3] , the new cross-bar switch can be used as a tunable multiplexer <i> and</i> demultiplexer. In addition to this more functional geometry, we present results demonstrating faster performance with a switching window of &ap;45 ps, corresponding to >20-GHz switching rates. We show a switching fidelity of >98%, i. e., switched polarization-encoded photonic qubits are virtually identical to unswitched photonic qubits. We also demonstrate the ability to select one channel from a two-channel quantum data stream with the state of the measured (recovered) quantum channel having >96% relative fidelity with the state of that channel transmitted alone. We separate the two channels of the quantum data stream by 155 ps, corresponding to a 6.5-GHz datastream. </p><p> Finally, we describe, develop, and demonstrate an application that utilizes the switch's higher-speed, lower-loss, and spatio-temporal-encoding features to perform quantum state tomographies on entangled states in higher-dimensional Hilbert spaces. Since many previous demonstrations show bipartite entanglement of two-level systems, we define "higher" as <i>d</i> > 2 where <i> d</i> represents the dimensionality of a photon. We show that we can generate and measure time-bin-entangled, two-photon, qutrit (<i>d</i> = 3) and ququat (<i>d</i> = 4) states with >85% and >64% fidelity to an ideal maximally entangled state, respectively. Such higher-dimensional states have applications in dense coding ^[4] , loophole-free tests of nonlocality ^[5] , simplifying quantum logic gates ^[6] , and increasing tolerance to noise and loss for quantum information processing ^[7] .</p>

<p> In this dissertation density functional theory (DFT) was applied to study the electronic structure and catalytic properties of graphene containing different types of defects. These defects includes hetero-atoms such as nitrogen, sulfur doped graphene, point defects such as Stone-Wales defects, single vacancy, double vacancies and substituting pentagon ring at zigzag edge, line defects such as pentagon-heptagon carbon ring chains, pentagon-pentagon-octagon carbon ring chains locating at the middle of graphene. The mechanisms of oxygen reduction reaction (ORR) were studied on these defective graphene, and electron transfer processes were simulated. Using DFT methods, we also explored the effect of strains to ORR electronic catalytic properties on pure and nitrogen doped graphene. </p><p> Our simulaltion results show that nitrogen, sulfur doped graphene, graphene containing point defects, substituting pentagon ring at zigzag edge, graphene containing line defects, pentagon-heptagon chain or pentagon-pentagon-octagon chains which have odd number of heptagon or octagon carbon ring perform high catalytic properties for ORR. Four electron transfer reactions could occur, and there are also two electrons transfer occuring on these defective graphene. The Stone-Wales defect itself cannot generate the catalytic activity on the graphene, but can facilitate the formation of hetero atom doping on graphene, which could show high catalytic activities to ORR. The catalytic active sites on defective graphene are atoms possessing high spin or charge density, where the spin density plays more important effect on the catalytic properties. For the N-doped graphene, the identified active sites are closely related to doping cluster size and dopant-defect interactions. Generally speaking, a large doping cluster size (number of N atoms >2) reduces the number of catalytic active sites per N atom. In combination with N clustering, Stone-Wales defects can strongly promote ORR. For four-electron transfer, the effective reversible potential ranges from 1.04 to 1.15 V/SHE, depending on the defects and cluster size. The catalytic properties of graphene could be optimized by introducing small N clusters in combination with material defects. For S-doped graphene, sulfur atoms could be adsorbed on the graphene surface, substitute carbon atoms at the graphene edges in the form of sulfur/sulfur oxide, or connect two graphene sheets by forming a sulfur cluster ring. Catalytic active sites distribute at the zigzag edge or the neighboring carbon atoms of doped sulfur oxide atoms, which possess large spin or charge density. For those being the active catalytic sites, sulfur atoms with the highest charge density take two-electron transfer pathway while the carbon atoms with high spin or charge density follow four-electron transfer pathway. Stone-Wales defects not only promote the formation of sulfur-doped graphenes, but also facilitate the catalytic activity of these graphenes. The ORR catalytic capabilities of the graphene containing point or line defects denpend on whether the defects could introduce spin density into the system or not. The axial strain field applied on the graphene could change its electronic properties. Neither the compressive nor the tensile strain along the zigzag or armchair direction could facinitate the catalytic activities of perfect graphene without any defects. Tensile strain along zigzag direction could change the electronic properties of nitrogen doped graphene, which are favorable to its ORR catalytic property. </p><p> Our simulation results explored the ORR on defective graphene in essence and provide the theoretical base for searching and fabricating new high efficient catalysts using the carbon based materials for fuel cells.</p>