Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 37 for “"quantum tunneling"”.
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Macroscopic quantum tunneling in superconducting nanowire devices
Macroscopic quantum tunneling is a process by which a macroscopic object, rather than a single electron, tunnels between two macroscopically distinct quantum states. In this dissertation, we will present the study of macroscopic quantum tunneling of phase-slips in superconducting devices, including …
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Quantum Tunneling of Charge-Density Waves in Quasi-One-Dimensional Conductors (Trichalcogenide, Tantalum Trisulfide, Niobium-Triselenide)
The charge-density wave (CDW) dynamics of the linear chain compound orthorhombic TaS(,3) is characterized by extensive measurements of dc conductivity, ac admittance, direct mixing, harmonic mixing, second harmonic generation, and third harmonic generation as functions of dc bias voltage, applied …
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Interband quantum tunneling at the band-edges in III-V semiconductor heterojunctions for low-power logic and detectors
This thesis explores interband tunneling in semiconductor heterojunctions where a density-of-states switching mechanism can be used to sharply modulate the junction conductance using small applied voltages via alignment and misalignment of the band-edges. Such a mechanism is useful for the pursuit …
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Thermal activation and macroscopic quantum phenomena in superconducting devices
… activation over the barrier and macroscopic quantum tunneling through the barrier. The measurements were performed for a variety of device parameters, corresponding to different shapes of the potential barrier. We find strong evidence for macroscopic quantum tunneling in both one and two …
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Probing quantum phase slips in superconducting nanowires modified using high bias voltage pulses
Quantum phase slips (QPS) or the macroscopic quantum tunneling (MQT) of a nanowire’s order parameter through an activation energy barrier have remained the subject of intense debate for many years. They are expected to occur at low enough temperature where thermally activated phase slips (TAPS) …
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Quantum Dynamics of Strong Field Light-Matter Interactions
… insights into long-debated problems related to quantum tunneling, namely, the quantum tunneling time and momentum i.e., the ongoing debate in the literature about how much time a particle spends in the classically forbidden region during the tunneling process and what is its momentum when it …
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Switching Current Distributions of Superconducting Nanowires: Evidence of Quantum Phase Slip Events
… is that phase slips should proceed via quantum tunneling events, which are known as quantum phase slips (QPS). However, experimental observation of QPS is a subject of strong debate and no consensus has been reached so far about the conditions under which QPS occurs. In this study, …
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Surface Friction and Spectroscopic Probes of New Physics with Trapped Ions
… vacuum is to control a microscopic, isolated quantum laboratory. This thesis describes two research programs made possible by single-ion trapping of Yb⁺. The first program is a study of a paradigmatic frictional interface: a trapped ion transported along a one-dimensional multistable energy …
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Electrical Resistance Studies of Hydrogen Diffusion and of Hydride Precipitation in Niobium
… undeformed data were fit to the Flynn-Stoneham quantum tunneling model of diffusion. The value for the lattice Debye temperature found was unphysically high (900 K); the validity of the model is therefore in question.
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A superconducting flux QuBit : measurement, noise and control
A superconducting quantum bit can be made with three nano-scale Josephson junctions connected in series. In this thesis, various aspects of this qubit are studied. It is shown numerically that the qubit behaves as a giant magnetic dipole with quantum tunneling between the two qubit states. The …
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Dynamics in neutron stars and the early universe
… pinning barriers through thermal activation or quantum tunneling, and ""creep"" slowly outward under forces created by the superfluid flow. To the extent that vortices remain pinned, the superfluid retains its angular momentum as the crust slows through interactions with its environment. …
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Topics in vacuum decay
… has more than one classically stable vacuum, quantum tunneling and thermal jumps make the transition between the vacua possible. The transition happens through a first order phase transition started by nucleation of a bubble of the new vacuum. The outward pressure of the truer vacuum makes the …
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Sensitive skins and somatic processing for affective and sociable robots based upon a somatic alphabet approach
… (temperature, electric field sensors, and Quantum Tunneling Composite (QTC) based force sensors) three dimensional sensor array was created as the first step in the design of the "sensitive skin" for the Huggable. A soft silicone skin was placed over this array. Preliminary results using …
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Semiclassical Propagators for Quantum Coherent States and Applications of Extra Quantum Phase to Large-spin Tunneling of Magnetic Molecules
… used to obtain the semiclassical expressions of quantum propagators by means of coherent states in the holomorphic representation together with the appropriate boundary conditions. It allows us to express the total actions including boundary terms, classical trajectories, and extra phases in the …
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Equilibrium and diffusion studies of metal-hydrogen systems
… diffusion which proceeds via lattice assisted quantum tunneling at room and lower temperatures requires a new and different description from the one based on the thermal hopping picture, which pertains only to relatively high temperatures. It is also shown that the analogs of the solution to …
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Quantum Resonant Beats and Revivals in the Morse Oscillators and Rotors
… Morse oscillator were applied to investigate the quantum resonant beats and revivals of wave packet propagation. A concise way for exact prediction of the complete revival period of the Morse oscillator was given for the first time. It was suggested that any complete period was made of integer …
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Tunneling Dynamics of a Bose-Einstein Condensate
… atoms make it an ideal system for studying Quantum Mechanical phenomenon like tunneling. This thesis describes progress towards experimentally measuring the time spent by a tunneling particle in the classically forbidden region. A detailed analysis of the experimental requirements to measure …
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Numerical calculations of the decay rate of a false vacuum for a modified quartic potential
… at any of these minima but is made unstable by quantum effects. The formalism that describes transitions from a false (higher energy density) vacuum to a true (lowest energy density) vacuum was developed decades ago. It suggests that false vacuum decay occurs via a quantum tunneling process, …
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A Single-Stage Passive Vibration Isolation System for Scanning Tunneling Microscopy
<p>Scanning Tunneling Microscopy (STM) uses quantum tunneling effect to study the surfaces of materials on an atomic scale. Since the probe of the microscope is on the order of nanometers away from the surface, the device is prone to noises due to vibrations from the surroundings. To minimize the …
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