Eric Sembrat's Test Bonanza

Obtaining a priori information on strongly interacting many-fermion systems remains a challenging problem in theoretical physics. A promising way forward is the use of Monte Carlo simulations, which are non-perturbative and take full account of quantum fluctuations. A famous example is Lattice QCD, which aims to elucidate the interactions between quarks and gluons at low energies, where QCD is strongly coupled. I will provide an update
on the application of such methods to closely related problems in condensed matter and atomic physics, highlighting modern computational and algorithmic developments. Specific examples include graphene and strongly coupled ultracold Fermi gases.

This workshop brings together researchers with an interest in soft materials, fluids, and biophysics to discuss their work and explore partnerships. All participants may present a sound bite (a few minutes).  The day will include breakfast, lunch, and coffee. Registration is free, but required.

Invited Speakers include M. Cristina Marchetti (Keynote Speaker, Syracuse University), Paul Goldbart (Georgia Tech), Juana Mendenhall (Morehouse College), Elisa Riedo (Georgia Tech), Susanne Ullrich (University of Georgia).

Location: Georgia Tech, Marcus Nanotechnology Building, Room 1116
Registration starts at 8:30 am; Workshop 9:00 am –5:30 pm

More information at: http://www.softmaterials.gatech.edu/workshops/sm5/

Some years ago an anomaly was noted in the decay of luminescence in certain doped alkali halides. The anomaly was eventually explained using a factor of a billion slowdown in lattice relaxation, a remarkable stretching of time scales. This slowdown was found to be caused by the creation of a ‘breather’ in the neighborhood of the dopant. Discrete breathers are nondispersive classical excitations that are known to be significant in many natural systems. In the talk I focus on the occurrence of breathers in doped alkali halides. Several more general properties of breathers have arisen from this study, among them is the quantum breather, a topic less fully explored than the classical theory because it does not yield easily to numerical simulation.

The homotopy theory of topological defects in ordered media fails to completely characterize systems with broken translational symmetry. We argue that the problem can be understood in terms of the lack of rotational Goldstone modes in such systems and provide an alternate approach that correctly accounts for the interaction between translations and rotations. Dislocations are associated, as usual, with branch points in a phase field, whereas disclinations arise as critical points and singularities in the phase field. We introduce a three-dimensional model for two-dimensional smectics that clarifies the topology of disclinations and geometrically captures known results without the need to add compatibility conditions. Our work suggests natural generalizations of the two-dimensional smectic theory to higher dimensions and to crystals.

Gamma-ray bursts have been detected at photon energies up to tens of GeV, and there are reasons to believe that the sources emit at least up to TeV energies, via leptonic or/and hadronic mechanisms. I review some recent developments in the GeV photon phenomenology in the light of Fermi observations, as well as recent related theoretical work. I discuss then the expected production of gravitational waves, the possibility of accelerating cosmic rays resulting in high energy neutrinos, and recent observational constraints.

Particle scattering processes at experiments such as the Large Hadron Collider at CERN are described by scattering amplitudes. In quantum field
theory classes, students learn to calculate amplitudes using Feynman diagram methods. This is a wonderful method for a process like electron +
positron -> muon^- + muon^+, but it is a highly challenging for a process like gluon+gluon -> 5 gluons, which requires 149 diagrams even at the leading order in perturbation theory. It turns out, however, that the result for such gluon scattering processes is remarkably simple, in some cases it is just a single term! This has lead to new methods for calculating scattering amplitudes, and it has revealed that amplitudes have a surprisingly rich mathematical structure. The applications of these new methods range from calculation of processes relevant for LHC physics to theoretical explorations of quantum gravity. I will give a pedagogical introduction to these new approaches to scattering theory and their applications, not assuming any prior knowledge of quantum field theory or Feynman rules.

As Goodyear discovered, when he first vulcanized rubber in 1839, a viscous liquid of macromolecules becomes an unusual, utterly random, solid, provided that enough chemical bonds are introduced between the molecules.  Perhaps surprisingly, given the randomness of their architectures, solids formed by the vulcanization process exhibit a number of rather simple and universal features -- both structural and elastic -- that are not exhibited by the apparently simpler, crystalline solids.  In this colloquium, I shall give an overview of current approaches to the physical properties of vulcanized matter and other random-network-forming media, paying special attention to their universal aspects.

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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 of
the 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 the dilute Fermi gas at unitarity using measurements of the sound absorption length.

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 routinely used in ion trap quantum information experiments. However, a similar interaction between ions held in separate trapping potentials (where the force is much weaker) has not been observed until now. I will discuss an experiment demonstrating coupling, at the quantum level, between two ions trapped in separate potential minima. The ions are confined to independent regions above a microfabricated, surface-electrode trap held at 4.2 K by a helium bath cryostat. This represents the first observation of coupling between quantized harmonic oscillators held in separate locations. Such an interaction may prove useful for quantum information processing, simulations, and metrology. The experiment also represents a first step toward hybrid quantum systems, such as coupling a trapped ion to a quantized mechanical oscillator. If time permits, I will also present very recent results verifying the exquisite level of control we have over single-qubit gates in this system.

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.