Events Archive

Apr
21
2011
"Coupled quantized harmonic oscillators" by Kenton Brown
In theory, quantum computers can solve certain problems much more efficiently than classical computers. This possibility has motivated experimental efforts to construct devices that manipulate quantum bits (qubits) in a variety of physical systems. One such system is composed of atomic ions confined by electric fields in a rf Paul trap. The motions of such ions can be modeled to a very good approximation as harmonic oscillators, and with suitable laser cooling techniques they can be cooled to the harmonic oscillator ground state. When trapped within the same potential minimum, ions interact strongly via the Coulomb force, thereby enabling multiple-qubit quantum gates that are...
Apr
20
2011
"Hydrodynamic Analogues of Quantum Systems" by John W.M. Bush
Yves Couder and coworkers have recently reported the results of a startling series of experiments in which droplets bouncing on a fluid surface exhibit wave-particle duality and, as a consequence, several dynamical features previously thought to be peculiar to the microscopic realm, including single-particle diffraction, interference, tunneling and quantized orbits. We explore this fluid system in light of the Madelung transformation, whereby Schrodinger's equation is recast in a hydrodynamic form. Doing so reveals a remarkable correspondence between bouncing droplets and subatomic particles, and provides rationale for the observed macroscopic quantum behaviour. New experiments are...
Apr
19
2011
"Thermal Conductivity, from Quark Matter to Cold Atoms" by Jingyi Chao
I briefly review the formation of color superconductivity which happens in compact stars. Below the temperature scale set by the gap in the quark spectrum, transport properties are determined by collective modes. We compute the thermal conductivity, $\kappa$, of color-flavor locked (CFL) quark matter in the frame of kinetics theory. We present and compare the result with previous estimates. We also conclude a CFL quark matter core ofthe compact star becomes isothermal on a timescale of a few seconds.  Moreover, we compute the thermal conductivity and sound attenuation length of a dilute Fermi gas, which help us comment on the possibility of extracting the shear viscosity of...
Apr
12
2011
"Relaxation of high-energy quasiparticles in a one-dimensional Bose liquid" by Prof. Michael Pustilnik
In this talk we will discuss a relaxation of high-energy quasiparticles in a weakly interacting one-dimensional Bose liquid. Unlike in higher dimensions, the rate is a nonmonotonic function of temperature. Moreover, it turns out that the inelastic scattering due to deviations from the integrability occurs at a much higher rate than three-body recombination processes, which is the main mechanism of losses in cold-atom-based realizations of 1D Bose liquids.
Apr
12
2011
"How Size and Strain Determine the Strength of Soft Materials" by Daniel Blair
Soft and biological materials often exhibit disordered and  heterogeneous microstructure. In most cases, the transmission and distribution of stresses through these complex materials reflects their inherent heterogeneity. We are developing a set of techniques that provide the ability to apply to quantify the connection between microstructure and local stresses.  We subject soft and biological materials to precise deformations while measuring real space information about the distribution and redistribution of stress. Using our custom confocal rheometer platform we can determine the role of shear stress in a variety...
Apr
12
2011
"Navier-Stokes solver using Green's functions" by Divakar Viswanath (Joint Physics & Math Seminar)
The incompressible Navier-Stokes equations provide an adequate physical model of a variety of physical phenomena. However, when the fluid speeds are not too low, the equations possess very complicated solutions making both mathematical theory and numerical work challenging. If time is discretized by treating the inertial term explicitly, each time step of the solver is a linear boundary value problem. We show how to solve this linear boundary value problem using Green's functions, assuming the channel and plane Couette geometries. The advantage of using Green's functions is that numerical derivatives are replaced by numerical integrals. However, the...
Apr
11
2011
"Towards optimal prediction of chaotic signals" by Divakar Viswanath
Abstract:  Suppose that x(t) is a signal generated by a chaotic system and that the signal has been recorded in the interval [0,T]. We ask: What is the largest value t_f such that the signal can be predicted in the interval (T,T+t_f] using the history of the signal and nothing more? We show that the answer to this question is contained in a major result of modern information theory proved by Wyner, Ziv, Ornstein, and Weiss. All current algorithms for predicting chaotic series assume that if a pattern of events in some interval in the past is similar to the pattern of events leading up to the present moment, the...
Apr
07
2011
"Localized states in one and two spatial dimensions" by Yi-Ping Ma
The 1:1 forced complex Ginzburg-Landau equation (FCGL) is a non-variational system that exhibits bistability between equilibria and thus admits traveling front solutions. A localized state consisting of an inner equilibrium embedded in an outer equilibrium can be formed by assembling two identical fronts back-to-back. In this talk, I will first describe the bifurcation structure of 1D steady localized states that takes the form of collapsed snaking (CS) if the inner equilibrium is temporally stable, and defect-mediated snaking (DMS) if the inner equilibrium is modulationally unstable. Outside their existence ranges, the steady localized states undergo time evolutions...
Apr
04
2011
"Collapse and stable self-trapping for Bose-Einstein condensates with 1/r^b type attractive interatomic interaction potential" by Pavel Lushnikov
We consider dynamics of Bose-Einstein condensates with long-range attractive interaction proportional to 1/r^b and arbitrary angular dependence. It is shown exactly that collapse of Bose-Einstein condensate without contact interactions is possible only for b greater or equal to 2. Case b=2 is critical and requires number of particles to exceed critical value to allow collapse. Case b>2 is supercritical with expected weak collapse which traps rapidly decreasing number of particles during approach to collapse. For b
Mar
31
2011
"Post-Shuttle Age: The Future of NASA": A Blended Research @ the Library panel discussion
Join us for the first Blended Research @ the Library panel discussion, Post-Shuttle Age: The Future of NASA.  Panelists are David Ballantyne, Assistant Professor in the School of Physics and the Center for Relativistic Astrophysics (CRA); Ashley Korzun, graduate student in the Daniel Guggenheim School of Aerospace Engineering; John Krige, Kranzberg Professor in the School of History, Technology and Society; and David Spencer, Professor in the School of Aerospace Engineering and Director of the Center for Space Systems.  They will be discussing the future of NASA after the end of the space shuttle program, touching on topics...

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