Physics Commons^™

Magnetic Order And Dimensional Crossover In Optical Lattices With Repulsive Interaction, Jie Xu

Dissertations, Theses, and Masters Projects

One of the most interesting and challenging problems in physics is understanding strongly correlated many-body systems, where strong interactions can yield many remarkable phenomena such as superfluidity in 4He, high-temperature superconductivity, etc. In order to attack these problems, we often need to reduce the complexity of the systems to simple models in hopes of getting better insights into the properties of the systems. The Hubbard model, the focus of this dissertation, is one of the most famous examples of such model, which describes a tunneling of electrons between nearest neighbor sites of a lattice with on-site interactions. This simple model …

A Tunable Electromagnetic Band-Gap Microstrip Filter, Greg A. Lancaster

Master's Theses

In high frequency design, harmonic suppression is a persistent struggle. Non-linear devices such as switches and amplifiers produce unwanted harmonics which may interfere with other frequency bands. Filtering is a widely accepted solution, however there are various shortcomings involved. Suppressing multiple harmonics, if desired, with traditional lumped element and distributed component band-stop filters requires using multiple filters. These topologies are not easily made tunable either. A new filter topology is investigated called Electromagnetic Band-Gap (EBG) structures.

EBG structures have recently gained the interest of microwave designers due to their periodic nature which prohibits the propagation of certain frequency bands. EBG …

Model Sensitivity In Holographic Superconductors And Their Deconstructed Cousins, Joshua X. Erlich, Zhen Wang

Arts & Sciences Articles

Holographic models of superconductors successfully reproduce certain experimental features of high-temperature superconductors, such as a large gap-to-Tc ratio compared to that of conventional superconductors. By deconstructing the extra dimension of these holographic models, similar phenomenology is described by a class of models defined in the natural dimension of the superconducting system. We analyze the sensitivity of certain observables in holographic and deconstructed holographic superconductors to details of the extra-dimensional spacetime. Our results support the notion that certain quantitative successes of simple models of this type are accidental. However, we also find a certain universal relationship between superconducting observables.

Quantum Cheshire Cats, Yakir Aharonov, Sandu Popescu, Daniel Rohrlich, Paul Skrzypczyk

Mathematics, Physics, and Computer Science Faculty Articles and Research

In this paper we present a quantum Cheshire Cat. In a pre- and post-selected experiment we find the Cat in one place, and its grin in another. The Cat is a photon, while the grin is its circular polarization.

An Effective Field Theory Calculation Of N(P, D)Γ Cross-Section For Big Bang Nucleo-Synthesis, Rasha Adnan Kamand

Theses and Dissertations

Studying the nuclear reaction n(p,d)γ and calculating its cross-section is not only a matter of interest from theoretical particle physics point of view but also from the viewpoint of cosmology. We now know that the universe is made up of only 5% baryonic matter. So, computing the density of baryons is of particular importance to physicists in general and cosmologists in particular. Deuterium production during Big Bang Nucleo-synthesis (BBN) is very sensitive to the density of baryons, thus baryon density can be inferred from the abundance of deuterium. In order to calculate deuterium abundance one needs to use the cross-section …

Quantifying The Impact Of Various Radioactive Background Sources On Germanium-76 Zero-Neutrino-Double-Beta-Decay Experiments, Katarina Leila Mizouni

Theses and Dissertations

The goal of searching for 0vBB-decay is to probe an absolute neutrino mass scale suggested by the mass-splitting parameters observed by neutrino oscillation experiments. Furthermore, observation of 0vBB-decay is an explicit instance of lepton-number non-conservation. To detect the rare events such as 0vBB-decay, half-lives of the order of 10^25-10^27 years have to be probed. Using an active detector with a large volume, such as hundreds of kilograms of HPGe in the case of MAJORANA, and taking efficient measures to mitigate background of cosmic and primordial origins are necessary for the success of a sensitive 0vBB-decay experiment.

One focus of the …

Landau-Zener Dynamics Of A Nanoresonator Containing A Tunneling Spin, Michael F. O'Keeffe, Eugene M. Chudnovsky, Dmitry A. Garanin

Publications and Research

We study the Landau-Zener dynamics of a tunneling spin coupled to a torsional resonator. For strong spin-phonon coupling, when the oscillator frequency is large compared to the tunnel splitting, the system exhibits multiple Landau-Zener transitions. Entanglement of spin and mechanical angular momentum results in abrupt changes of oscillator dynamics which coincide in time with spin transitions. We show that a large number of spins on a single oscillator coupled only through the in-phase phonon field behaves as a single large spin, greatly enhancing the spin-phonon coupling. We compare purely quantum and semiclassical dynamics of the system and discuss their experimental …

Quantum Dynamics Of Vortices In Mesoscopic Magnetic Disks, Ricardo Zarzuela, Eugene M. Chudnovsky, J M. Hernandez, J Tajeda

Publications and Research

Model of quantum depinning of magnetic vortex cores from line defects in a disk geometry and under the application of an in-plane magnetic field has been developed within the framework of the Caldeira-Leggett theory. The corresponding instanton solutions are computed for several values of the magnetic field. Expressions for the crossover temperature Tc and for the depinning rate \Gamma(T) are obtained. Fitting of the theory parameters to experimental data is also presented.

Turbulent Fronts Of Quantum Detonation In Molecular Magnets, Dmitry A. Garanin

Publications and Research

Dipolar-controlled quantum deflagration going over into quantum detonation in the elongated Mn_12 Ac molecular magnet in a strong transverse field has been considered within the full 3d model. It is shown that within the dipolar window around tunneling resonances the deflagration front is non-flat. With increasing bias, dipolar instability makes the front turbulent, while its speed reaches sonic values, that is a signature of detonation.

Mutual Information In Hawking Radiation, Norihiro Izuka, Daniel N. Kabat

Publications and Research

We compute the mutual information of two Hawking particles emitted consecutively by an evaporating black hole. Following Page, we find that the mutual information is of order exp(-S) where S is the entropy of the black hole. We speculate on implications for black hole unitarity, in particular on a possible failure of locality at large distances.

Black Hole Formation In Fuzzy Sphere Collapse, Norihiro Izuka, Daniel N. Kabat, Roy Shubho, Debajyoti Sarkar

Publications and Research

We study the collapse of a fuzzy sphere, that is a spherical membrane built out of D0-branes, in the BFSS model. At weak coupling, as the sphere shrinks, open strings are produced. If the initial radius is large then open string production is not important and the sphere behaves classically. At intermediate initial radius the back-reaction from open string production is important but the fuzzy sphere retains its identity. At small initial radius the sphere collapses to form a black hole. The crossover between the later two regimes is smooth and occurs at the correspondence point of Horowitz and Polchinski.

Black Hole Formation At The Correspondence Point, Norihiro Izuka, Daniel N. Kabat, Roy Shubho, Debajyoti Sarkar

Publications and Research

We study the process of bound state formation in a D-brane collision. We consider two mechanisms for bound state formation. The first, operative at weak coupling in the worldvolume gauge theory, is pair creation of W-bosons. The second, operative at strong coupling, corresponds to formation of a large black hole in the dual supergravity. These two processes agree qualitatively at intermediate coupling, in accord with the correspondence principle of Horowitz and Polchinski. We show that the size of the bound state and timescale for formation of a bound state agree at the correspondence point. The timescale involves matching a parametric …

Cft Representation Of Interacting Bulk Gauge Fields In Ads, Daniel N. Kabat, Gilad Lifschytz

Publications and Research

We develop the representation of interacting bulk gauge fields and charged scalar matter in AdS in terms of non-local observables in the dual CFT. We work in holographic gauge in the bulk, A_z = 0. The correct statement of micro-causality in holographic gauge is somewhat subtle, so we first discuss it from the bulk point of view. We then show that in the 1/N expansion CFT correlators can be lifted to obtain bulk correlation functions which satisfy micro-causality. This requires adding an infinite tower of higher-dimension multi-trace operators to the CFT definition of a bulk observable. For conserved currents the …

Reversal Of Magnetization Of A Single-Domain Magnetic Particle By The Ac Field Of Time-Dependent Frequency, Liufei Cai, Dmitry A. Garanin, Eugene M. Chudnovsky

Publications and Research

We report numerical and analytical studies of the reversal of the magnetic moment of a single- domain magnetic particle by a circularly polarized ac field of time-dependent frequency. For the time-linear frequency sweep, the phase diagrams are computed that illustrate the dependence of the reversal on the frequency sweep rate v , the amplitude of the ac field h , the magnetic anisotropy field d , and the damping parameter . It is shown that the most efficient magnetization reversal requires a non-linear time dependence of the frequency, ! ( t ) , for which an exact analytical formula is …

Excitation Modes Of Vortices In Submicron Magnetic Disks, Ricardo Zarzuela, Eugene M. Chudnovsky, Javier Tejada

Publications and Research

Classical and quantum theory of spin waves in the vortex state of a mesoscopic sub-micron magnetic disk has been developed with account of the finite mass density of the vortex. Oscillations of the vortex core resemble oscillations of a charged string in a potential well in the presence of the magnetic field. Conventional gyroscopic frequency appears as a gap in the spectrum of spin waves of the vortex. The mass of the vortex has been computed that agrees with experimental findings. Finite vortex mass generates a high-frequency branch of spin waves. Effects of the external magnetic field and dissipation have …

On Three Dimensions As The Preferred Dimensionality Of Space Via The Brandenberger-Vafa Mechanism, Brian Greene, Daniel N. Kabat, Stefanos Marnerides

Publications and Research

In previous work it was shown that, in accord with the Brandenberger-Vafa mechanism, three is the maximum number of spatial dimensions that can grow large cosmologically from an initial thermal fluctuation. Here we complement that work by considering the possibility of successive fluctuations. Suppose an initial fluctuation causes at least one dimension to grow, and suppose successive fluctuations occur on timescales of order alpha'^{1/2}. If the string coupling is sufficiently large, we show that such fluctuations are likely to push a three-dimensional subspace to large volume where winding modes annihilate. In this setting three is the preferred number of large …

Diffractive Effects And General Boundary Conditions In Casimir Energy, Dimitra Karabali, V P. Nair

Publications and Research

The effect of edges and apertures on the Casimir energy of an arrangement of plates and boundaries can be calculated in terms of an effective nonlocal lower-dimensional field theory that lives on the boundary. This formalism has been developed in a number of previous papers and applied to specific examples with Dirichlet boundary conditions. Here we generalize the formalism to arbitrary boundary conditions. As a specific example, the geometry of a flat plate and a half-plate placed parallel to it is considered for a number of different boundary conditions and the area-dependent and edge dependent contributions to the Casimir energy …

Nanoparticle Self-Assembly And Ultrafast Nanomagnet Switching Dynamics, Longfei Ye

Theses and Dissertations

A novel manufacturing technology that offers a low-cost alternative for creating more complex optical materials that are assembled with single-nanometer precision is demonstrated. Using the enormous magnetic field gradients present near the surface of magnetic recording media, colloidally suspended superparamagnetic nanopartilces are self-assembled into patterned microstructures.

The position and shape of these microstructures are precisely controlled by magnetic patterns on the template. The template that can be reprogrammed and reused is magnetically recorded using commercial magnetic recording technology. These microstructures consisting entirely of self-assembled magnetic nanoparticles are then transferred to flexible polymer thin films with patterns maintained. In particular, all-nanoparticle …

Versatile Rb Vapor Cells With Long Lifetimes, John F. Hulbert, Matthieu Giraud-Carrier, Tom Wall, Aaron R. Hawkins, Scott D. Bergeson, Jennifer Black, Holger Schmidt

Faculty Publications

The authors report on an approach to the construction of long-lasting rubidium atomic vapor cells. The method uses pinch-off copper cold-welds, low temperature solders, and electroplated copper to create long-lasting hermetic seals between containment chambers of dissimilar geometries and materials. High temperature epoxy, eutectic lead/tin solder, and indium solder were considered as sealing materials. These seals were analyzed using accelerated lifetime testing techniques. Vapor cells with epoxy and bare metal solder seals had a decrease in the rubidium atomic density within days after being heated to elevated temperatures. They also exhibited broadened spectra as a result of rubidium reacting with …

Dipolar Interactions, Long Range Order And Random Fields In A Single Molecule Magnet, Mn12-Acetate, Bo Wen

Dissertations, Theses, and Capstone Projects

In this thesis, I will present an experimental study of two single molecule magnets, Mn₁₂-ac and Mn₁₂-ac-MeOH. I will show that in both systems, the temperature dependence of the inverse susceptibility yields a positive intercept on the temperature axis (a positive Weiss temperature), implying the existence of a ferromagnetic phase at low temperature.

Applying a magnetic field in the transverse direction moves the Weiss temperature downward towards zero. This implies that the transverse field triggers mechanisms in the system that compete with the dipolar interaction and suppress the long-range ordering.

I will then show that the …