Physics

Running Shor's Algorithm on a complete, gate-by-gate implementation of a virtual, universal quantum computer

Yunseong Nam — Tue, 19 Jun 2012 09:26:46 PDT

Exploiting Wave Transport in PT Symmetric Media

Zin Lin — Tue, 19 Jun 2012 09:18:35 PDT

This thesis will present an integrated experimental and theoretical effort toward managing wave transport and introducing novel methods for signal manipulation. This will be achieved by developing a new circuitry design that exploits both absorption and gain mechanisms via judicious spatial arrangements of active elements that exhibit space-time reflection, or PT symmetries. We will show that the resulting structures, display intriguing behaviour that holds promises for the creation of new synthetic matter with novel functionalities. The playing field will be photonic and electronic circuits with complex potentials corresponding to complex refraction index and active impedances respectively.

Two Point Correlations Between Velocity Sums and Differences, and Their Implications for Large-Small Scale Correlations in Fluid Turbulence

Nicholas Joseph Rotile — Tue, 19 Jun 2012 09:01:11 PDT

Trends in Time-of-Flight Parameters with Application to Autoionization Lifetime Measurements

Seth Michael Hafferkamp — Tue, 19 Jun 2012 08:45:12 PDT

Extraction of Atom-Diatom Collision Properties by Least Squares Fitting

James Paris Wampler — Thu, 02 Jun 2011 13:36:44 PDT

Experimental Measurement of the Stress Tensor in a Quasi-2D Granular Gas

Wan Jun Yang — Thu, 02 Jun 2011 13:29:47 PDT

Dynamic Vortex Drag

Nicholas Everett Jackson — Thu, 02 Jun 2011 13:27:24 PDT

This thesis explores the concept of dynamic vortex drag resulting from Kelvin wave excitations on vortex cores in thin films of superfluid ^{4}He. In this system, vortex drag is commonly accepted as a significant mechanism for the dissipation of third sound wave motion; however, current models implementing a static drag force have been unable to quantitatively explain anomalous third sound free decay results found in the literature. In this thesis, many possible manifestations of Kelvin wave agitation are explored and are shown to correct the deficiencies of existing static drag theories. It is therefore concluded that vortex drag in thin films of superfluid ^{4}He is most likely a dynamic, and not a static, process.

Chaos at the Crossroads of Spontaneous Symmetry Breakings: Novel Universality Classes

Carl Tonner West — Thu, 02 Jun 2011 13:10:42 PDT

This thesis investigates quantum systems with underlying classically chaotic dynam- ics in the framework of spontaneous symmetry-breaking transitions. The main emphases are on: (i) Quantum-Classical correspondence in systems at a metal-to-insulator tran- sition as seen through dynamical stability with respect to external perturbations, and (ii) the spontaneous breaking of combined parity and time-reversal symmetry in non- Hermitian systems across the localization-delocalization transition. By studying such crossroads between a critical phase transition and a parametric system change (quan- tum to classical or localized to delocalized) we are able to develop results for entire universality classes.

Effect of Valency on the Dynamics and Thermodynamics of DNA-linked Nanoparticles Materials

Wei Dai — Thu, 17 Jun 2010 11:35:37 PDT

Nanoparticles (NP) functionalized with single-stranded DNA (ssDNA) offer a route to custom-designed, self-assembled nanomaterials with potentially unusual properties. We explore the phase behavior and structure of a model for NP functionalized with between 3 and 6 short ssDNA through simulations, allowing us to examine both the role of the number of attached strands (valency) and their relative orientations. We find that 3 to 5-functionalized NP form amorphous systems, with 4 and 5-functionalized NP constructing an unusual multitude of liquid phases, or polyamorphism, through interpenetration of networks. The 6-functionalized NP with octahedral symmetry form at least six crystalline structures, consisting of up to six interpenetrating simple cubic lattices. The crystallization dynamics of the 6-functionalized system follows the conventional two-step pathway, demonstrating that such mechanism applies to our NP system with complex interactions.

Stability of DNA-Linked Nanoparticle Crystals

Olivia Padovan-Merhar — Thu, 17 Jun 2010 11:35:12 PDT

In this thesis, a coarse-grained molecular dynamics model is used to address three factors which impact the kinetic and thermodynamic stability of BCC and FCC crystals formed in DNA-linked nanoparticle systems: (i) surface mobility, (ii) the number of attached strands, and (iii) the size of the nanoparticle core. The model predicts that systems with surface mobility form crystals with lower free energy, but also a lower heat of fusion. FCC crystals have a higher kinetic melting temperature when formed in systems with low surface mobility, but BCC crystals have a lower kinetic melting temperature when formed in systems with low surface mobility. The model demonstrates that the kinetic melting temperature of BCC and FCC systems increases with increasing number of strands, but that it decreases with increasing core size. The results presented here are intended to provide guidance in the choice of parameters when experimentally forming crystals.

Non-Hermitian Dynamics: Examples from Disordered Microwave Cavities and Classical Optics

Mei Chai Zheng — Thu, 17 Jun 2010 11:34:08 PDT

This thesis investigates dynamics in leaking systems with and without amplification. On the one hand, we introduce and investigate both theoretically and experimentally a new measure of Anderson localization in random media which takes absorption into account. On the other hand, we study wave propagation in a new class of synthetic optical materials (periodic or random) where gain and loss are judiciously tailored. These two seemingly different types of problems are nicely brought together in the framework of non-Hermitian Hamiltonian formalism.

Experimental Study of Lagrangian Velocity and Energy Statistics in Inhomogeneous Turbulence

Surendra Bahadur Kunwar — Thu, 17 Jun 2010 11:33:53 PDT

We study Lagrangian statistics in a flow stirred by two oscillating grids. We quantify the dependence of small scales on the inhomogeneous large scales in a complex flow. We also describe the method we developed to study the measurement volume bias while investigating Lagrangian structure functions. We identify the important factors in energy transport by estimating the terms of the turbulent kinetic energy equation.

Granular Gravitational Collapse in Realistically Simulated Granular Gases

Samuel Benjamin Kachuck — Thu, 17 Jun 2010 11:33:39 PDT

Gravitational granular collapse (GGC) occurs whenever a granular gas is allowed to evolve freely in gravity without the additional input of kinetic energy. The system dissipates its remaining energy through inelastic collisions as it settles into a granular solid at rest at the bottom of its enclosure in &#64257;nite time. We are interested in the reasons for an observed divergence between experimental and theoretical results of the rate of decay. The use of realistic simulations con&#64257;rms that, even in more closely ideal settings, the theory is not as universal as expected. We test the relative e&#64256;ects of a variety of system parameters on GGC dynamics and conclude that the second-power granular temperature decay law during GGC theoretically derived involves the somewhat unphysical approximation of particles that interact with a constant coe&#64259;cient of resititution that is very far into the elastic limit.

Self-Assembly of DNA-Linked Nanoparticles

Chia Wei Hsu — Thu, 17 Jun 2010 11:32:50 PDT

Nanoparticles (NP) tethered with DNA strands can self-assemble into highly organized structures through complementary bonding of base pairs. Such materials are promising building blocks for the bottom-up nanotechnology. This thesis investigates (a) the phase diagram of NP tethered with four DNA strands, (b) lattice models that reveal the insights behind the unusual phase behavior, and (c) a theoretical description for the self-assembly. All of our studies are based on a combination of theory and simulations. We report the discovery of a hierarchy of amorphous networked phases that has never been observed in other materials. The mechanism behind the multitude of phases is studied in detail using various approaches. Lastly, we present a comprehensive theoretical framework that quantitatively describes the equilibrium clustering and dynamics, as well as the self-assembly kinetics. The theoretical predictions yield striking agreement with our molecular modeling.

Investigation of Stark Broadening in LIBS of Hydrogen Balmer emission lines n = 3 to 15

Yudhishthir Prasad Kandel — Wed, 27 May 2009 12:36:25 PDT

This thesis investigates Stark broadening hydrogen Balmer emission lines n = 4 to 15 subsequent to nanosecond laser induced optical breakdown of hydrogen gas from Nd:YAG Q-switched laser operated at 1064 nm. Data for 1, 2 and 4 µs delay times after the plasma initiation was Abel inverted for Balmer emission lines from n = 3 to 10. Trends in Area and FWHM under the fitted Lorentzian to these curves were plotted as a function of radius and for three separate delays. Temperature of 5000 to 10000 K was calculated. Electron number of density of 5×&#12310;10&#12311;^16 to 1×&#12310;10&#12311;^15/&#12310;cm&#12311;^(-3)was referred from the theory. This work was able to observe distinguishable hydrogen Balmer emission lines from plasma for n = 3 to 15.

Vortex Dissipation in Superfluid Third Sound Flows

Anand Swaminathan — Wed, 27 May 2009 12:34:07 PDT

This thesis probes possible mechanisms behind anomalous freedecays commonly observed in superfluid helium third sound flows. Several models, based on vortex dissipation, for the additional dissipation these anomalous freedecays imply are constructed, tested, and modified to be consistent with the observed characteristics. This work concludes that these simple models involving only vortex friction and a creation energy are insufficient to explain the observed characteristics. From this conclusion a model is proposed that holds promise for future study.

Wave-packet Dynamics in Unconventional RMT Models

James Maxwell Aisenberg — Wed, 27 May 2009 12:33:35 PDT

We analyze the wave-packet dynamics scenario produced by Random Matrix Theory models with unconventional band-profile structures. Our motivation is to understand the energy spreading of quantum systems with complex dynamics. Examples of such systems include complex nuclei, atoms and molecules, quantum dots, and Bose-Einstein Condensates in optical traps, which, under the influence of an external perturbation, experience an energy redistribution of the initially prepared state. Such a perturbation could be due to an external electric or magnetic field, a change in the confining geometry, or a residual interaction, among other things. Of special interest in our analysis is the investigation of the time relaxation properties of a prepared state into a sea of other states (the continuum). We find that, for a large family of power spectra characterized by a non-flat profile, the survival probability $P(t)$ might exhibit either exponential-like or power-law decay.

Conductance of Mesoscopic Rings

Rangga Perdana Budoyo — Mon, 30 Jun 2008 08:58:40 PDT

In the studies of conductance of closed mesoscopic systems, semilinear response theory offers a novel unified framework that goes beyond the traditional Kubo formulation. Here we apply SLRT to two mesoscopic systems. The first is disordered quasi-1d rings, where we build an analytical model to understand the departure of SLRT from Kubo results. Guided by the numerical analysis on the statistical properties of the current operator matrix elements, we introduce a random matrix theory model which leads to a generalized variable range hopping picture of the conductance. Both of these models capture the essential aspects of the mesoscopic conductance for this system. The second one is the Harper model, which is a one-dimensional model that exhibits a Metal-Insulator transition--at the critical point, it possesses fractal structures in both the eigenfunctions and the eigenvalues. We are interested in studying how the fractal structures might have an effect on the conductance.

The Role of Limited Valency and Bonding Orientation on Phase Behavior

Zhi Da Henry Tan — Mon, 30 Jun 2008 08:58:38 PDT

Nanoparticles functionalized by single strands of DNA have been shown to be highly customizable building blocks for self-assembled nano-structures, giving rise to complex networks that have very unusual phase diagrams. Specifically, the nanoparticles exhibit a phase diagram which contains three critical points; the presence of two critical points is rare in nature, but has been found in some natural substances like water. In this thesis, we use lattice models to examine which nearest neighbor interactions are important to generate multiple distinct phases. We show that the multiple critical points cannot be reproduced via limiting the number of bonding neighbors alone. Development of more complex lattice models that may include such behavior based on our results is ongoing.

Comparison of Molecular and Gravitational Three-Body Collisions

Aaron Nicholas Larner — Mon, 30 Jun 2008 08:58:17 PDT