Colloquium Archives

Bei-Lok HU, University of Maryland

Topic: "Understanding Macroscopic Quantum Phenomena*"  (Video)

Abstract: Macroscopic quantum phenomena refer to quantum features in objects of `large' sizes, systems with many components or degrees of freedom, organized in ways where they can be identified as `macroscopic’ objects. This emerging field is ushered in by several categories of definitive experiments in superconductivity, electromechanical systems, Bose-Einstein condensates and others. Yet this new field which is rich in open issues at the foundation of quantum and statistical physics remains little explored theoretically (with the notable exception of Leggett [0]). This talk summarizes our thoughts while attempting a systematic investigation into some key foundational issues of quantum macroscopic phenomena with the goal of ultimately revealing or building a viable theoretical framework.

Dominik Schneble, Stony Brook University

Topic: "Exploring Atomic Matter-Wave Dynamics in Lattice Potentials"  (Video)

Abstract: Ultracold atomic gases in optical lattices allow for a wide range of studies at the boundary between atomic and condensed-matter physics. In my talk I will discuss three very distinct experiments that involve lattice-induced diffraction of atomic matter waves derived from a Bose-Einstein condensate. In the first experiment, using a state-dependent lattice potential, we demonstrated a novel type of atomic four-wave mixing in a binary atomic mixture. In the second experiment, using a pulsed incommensurate lattice, we realized a system of coupled kicked quantum rotors in which we observed a quantum-to-classical transition. In the third experiment, we showed that Bragg diffraction of atoms can be used to probe artificial atomic crystals, in analogy to neutron diffraction from conventional solids.

Lawrence Schulman, Clarkson University

Topic: "Time: Problems and Arrows"  (Video)

Abstract: After briefly reviewing some of the physicist's many problems with time, I focus on issues surrounding the "arrow of time," the directionality that dominates much of physics, and indeed almost everything else. By formulating the arrow as a preference for one kind of boundary problem over another, different thermodynamic scenarios are explored. In particular I examine situations in which regions with opposite pointing arrows could mutually survive. Simulations and other methods suggest that there could be observational tests of the presence of such matter. Signalling in a limited sense is also possible.

John Delos, The College of William & Mary

Topic: "Electronic Detection and Diagnosis of Health and Illness of Premature Infants"  (Video)

Abstract: The pacemaking system of the heart is complex; a healthy heart constantly integrates and responds to extracardiac signals, resulting in highly complex heart rate patterns with a great deal of variability. In the laboratory and in some pathological or age related states, however, dynamics can show reduced complexity that is more readily described and modeled. Reduced heart rate complexity has both clinical and dynamical significance – it may provide warning of impending illness or clues about the dynamics of the heart’s pacemaking system. Here we describe simple and interesting heart rate dynamics that we have observed in premature human infants – reversible transitions to large-amplitude periodic oscillations – and we show that they give early warning of bacterial infections in premature infants, and we show that the appearance and disappearance of these periodic oscillations can be described by a simple mathematical model, a Hopf bifurcation.

Eric Heller, Harvard University

Topic: "Branched flow of waves and rays in quantum mechanics, oceanography, acoustics, and more"  (Video)

Abstract: The familiar twinkling of starlight or the pattern of sunlight on a pool bottom is the beginning of the phenomenon of branched flow, which applies to both waves and rays. It is a beautiful and poorly studied phenomenon, given its ubiquity. We illustrate, explain, and discuss the applicability across many fields of science.

David Ballantyne, Georgia Institute of Technology

Topic: "Connecting Star Formation, Galaxy Evolution and the X-ray Background"  (Video)

Abstract: As we now know, the growth of galaxies and their central black holes is connected through some unknown mechanism. The cosmic X-ray background encodes within it the entire history of accretion onto supermassive massive black holes and so provides an unique view of the role of AGN in the assembly of galaxies. This talk presents results of recent work that is attempting to exploit the information contained in the X-ray background (and ancillary multiwavelength studies) to construct a testable scenario for the evolution of AGN and their host galaxies.

David Cory, IQC Waterloo

Topic: "A Path Towards a Quantum Computer" (Video)

Abstract: Quantum mechanics is the ultimate law of nature and when we engineer devices to function uniquely quantum mechanically then we reach the ultimate efficiency allowed by nature. For many interesting tasks this quantum efficiency greatly exceeds that of classical devices. Today we are developing quantum sensors, actuators and information processors, moving along a path that we hope will take us to a quantum computer. I will describe one such path using a hybrid processor of superconductors, electron and nuclear spins.

Robyn Millan, Dartmouth College

Topic: "Dynamics of Radiation Belt Electrons and the BARREL Experiment" (Video)

Abstract: The intensity of relativistic electrons in Earth's radiation belts is known to be highly variable, but the processes responsible for this variability are still not well understood. Observed rapid depletions and subsequent rebuilding of the trapped particle population imply an efficient energization process, in some cases accelerating electrons to multiple MeV energies on a timescale as short as minutes. NASA's two Van Allen Probes were launched in August 2012 to study the radiation belts. BARREL is a multiple-balloon investigation that works with the Van Allen Probes to study atmospheric loss of radiation belt electrons. The first BARREL balloon campaign was carried out in January-February 2013. Twenty small (~20 kg) balloon payloads were launched from the SANAE IV and Halley VI Antarctic research stations. A second campaign will be carried out next year. This talk will provide an introduction to radiation belt physics, and will summarize early results from BARREL and Van Allen.