Fall 2007
Click colloquium title to view complete abstract in PDF file format.
Speaker: Professor Joel Primack,Professor of Physics, UCSC
Abstract:
Before 2004, NASA's Beyond Einstein program included ambitious space missions to understand the nature of the dark energy that has been accelerating the expansion of the universe, test general relativity, and discover gravity waves from the mergers of supermassive black holes and from the cosmic inflation that preceded the Big Bang. All of these, plus space missions to map our home galaxy and investigate whether planets around other stars have life, were indefinitely postponed when President Bush decided in January 2004 that NASA's highest priority is to put astronauts back on the moon and eventually send them to Mars. Under pressure from Congress, the National Academy of Sciences was commissioned in 2006 to report on how to restart the Beyond Einstein program. This colloquium by one of the members of this recently released Academy study will summarize and explain the research strategy the report proposes and its implications for continued U.S. participation in the exploration of the universe.
Speaker: Ernst Sichtermann, Lawrence Berkeley National Laboratory
Title:"Muon g-2"
Abstract:
The magnetic moments and g-values of particles have played important roles in the development of modern physics.
Speaker: Professor Gordon Kane, University of Michigan and Institute for Advanced Study
Title: "String theory and the real world"
Abstract:
I'll describe how string theory is being connected to testable predictions, via the increasingly active subfield "string phenomenology". Examples will include issues from cosmology (dark matter, inflation, and dark energy), neutrino masses, and particularly collider physics and the possible role of the LHC. The talk will be organized around a list of questions particle physics and cosmology hope to answer about the laws of nature and the universe, and how string theory is beginning to address (all?) these questions.
Speaker: Professor David Goldhaber-Gordon, Assistant Professor of Physics, Stanford University
Title: "Designer Hamiltonians in the Laboratory: Observation of Many Body Physics in a Semiconductor Nanostructure"
Abstract:
Physicists and material scientists have long designed materials with
remarkable and varied electronic behaviors, from charge-density waves
to high-temperature superconductivity. Much of the most intriguing
phenomena involves highly correlated electron physics - the motion of
one electron dramatically effects the motion of surrounding electrons.
A classic example of this is the two- channel Kondo system, where a
local magnetic moment is screened by two independent conduction
reservoirs.
Following a proposal by Oreg and Goldhaber-Gordon, I will discuss
an experimental realization of the two- channel Kondo Hamiltonian in a
semiconductor nanostructure. With a geometry of two coupled quantum
dots in a 2D electron system, we are able to tune in situ the
parameters of the two channel Kondo model. Using electrostatic gates,
we tune continuously between two distinct Fermi liquid regimes, which
are characterized by different values of conductance through the
nanostructure. We investigate the properties of this uantum phase
transition and the associated two- channel Kondo quantum critical point.
Speaker: Professor Sankar Das Sarma, University of Maryland
Title: "Computing with quantum knots: Non-Abelian anyons and topological quantum
computation"
Abstract:
Ordinary quantum computation uses simple quantum two level systems (e.g. electron or nuclear spins, atomic hyperfine states, etc.) as quantum bits (‘qubits’) with one- and two-qubit unitary operations serving as universal quantum gates. The main problem is quantum decoherence, the inevitable continuous leakage of a quantum state due to its interaction with the environment. Very stringent quantum error correction protocols, i.e. quantum noise reduction procedure, must be employed to keep such qubit states alive and coherent during the computation. In sharp contrast to such noise-reduced quantum computation, a revolutionary alternative idea is to build an effectively ‘deaf’ quantum computer which is topologically immune to quantum decoherence. Such an inherently fault tolerant topological quantum computer is completely protected from any local perturbation induced by the environment and uses the time-space braiding (i.e. creating suitable quantum knots) of non-Abelian anyonic quasiparticles for quantum computation. The topological quantum computer is thus a ‘natural’ quantum computer where local quantum errors are suppressed at the hardware level due to the non-local topological nature of the ground state, thus completely eliminating the need or necessity for any software-based quantum error correction. Whether such a fault-tolerant natural topological quantum computer can be built or not depends on the existence in nature of suitable topological quantum phases of matter and our ability to manipulate and braid their non-Abelian anyonic quasiparticles. Prospects for topological quantum computation will be discussed critically in this talk from a combined experimental and theoretical perspective. I will discuss a number of physical systems, e.g. fractional quantum Hall states, chiral p-wave superconductors, p-wave cold atom superfluids, suitably designed cold atom optical lattices, frustrated quantum magnetic systems, Josephson junction arrays, rotating BEC systems, etc. where the possibility for doing topological quantum computation has been discussed in the recent literature. I will provide a perspective on how realistic such ideas are and discuss the (very difficult) physics issues which would have to be addressed before laboratory topological quantum computation can happen. I will also provide an elementary introduction to the concepts of topological phase, anyons, and non-Abelian braiding statistics. The interdisciplinary subject of topological quantum computation brings together topology, conformal field theory, fractional quantum Hall effect, Chern-Simons-Witten theory, and materials science.
Speaker: Saul Teukolsky, Hans A. Bethe Professor of Physics and Astrophysics, Cornell University
Title: Black Holes and Gravitational Waves
Abstract:
Gravitational wave detectors like LIGO are poised to begin detecting signals. One of the prime scientific goals is to detect waves from the coalescence and merger of black holes in binary systems. Confronting such signals with the predictions of Einstein's General Theory of Relativity will be the first real strong-field test of the theory. Until very recently, theorists were unable to calculate what the theory actually predicts. I will describe recent breakthroughs that have occurred and that have set things up for an epic confrontation of theory and experiment.
Speaker: Geralyn Sam Zeller, Los Alamos National Laboratory
Title:“MiniBooNE: Not Just for Neutrino Oscillations Anymore ”
Abstract:
The MiniBooNE experiment at Fermilab has amassed the world's largest
sample of neutrino scattering events in the 1 GeV energy range; a
sample that includes both quasi- elastic scattering and single pion
production processes. Although the primary motivation for MiniBooNE has
been the now-reported search for muon neutrino to electron neutrino
oscillations, there has been recent regained interest in neutrino
interaction physics. Such low energy neutrino cross section
measurements have not been updated for decades, having been first
measured in bubble chamber experiments. New measurements are sorely
needed and yield important constraints for neutrino oscillation
experiments, including MiniBooNE. With an order of magnitude larger
statistics than historically available, study of the MiniBooNE events
is already providing new insight into low energy neutrino scattering on
nuclei. In addition to these neutrino results, preliminary findings
will also be shown from a new MiniBooNE antineutrino data sample
collected in the past year.
Speaker: Alessandra Lanzara, Professor of Physics, University of California, Berkeley
Title:"Dirac particles in a pencil trace"
Abstract:
The recent discovery of graphene, a two dimensional carbon crystal, has
generated a lot of excitement in condensed matter community because of
its unusual electronic properties as well as its potential
applications. The secret lies in the relativistic character of its
charge carriers, which make graphene the ideal system where
relativistic quantum physics and condensed matter physics meets. We
will present an overview of the electronic properties of Dirac
quasiparticle in graphene and discuss its similarities with high
temperature superconductors. The great potential of graphene films for
next generation electronic devices is discussed.
Speaker: Massimo Porrati, Professor of Physics, New York University
Title: "The Invisible Hand, or How String Theory Changed Our View of the Visible Universe"
Abstract:
After a brief reminder of the basic concepts of string theory, We will
review a few ideas in today's theoretical physics which either
originated or were made plausible by string theory. Through those
examples, I will argue that string theory provides a deep unifying
framework, a common language if you wish, for describing and justifying
some of the most basic as well as some of the most exciting ideas in
high energy theoretical physics.
Speaker: Anatoly Spitkovsky, Assistant Professor of Astrophysical Sciences, Princeton University
Title:Extreme magnetospheres: from pulsars to accretion disks
Abstract:
Many astrophysical objects, including neutron stars and accretion
disks, are commonly interpreted as strongly magnetized conducting
bodies rotating in the presence of plasma. Our ability to model
magnetospheres of such objects has been hampered by the difficulty of
solving the self-consistent behavior of strongly magnetized
relativistic plasmas. I will describe the recent progress in numerical
modeling of magnetically-dominated plasmas and present applications to
several sources of interest. First, I will present the numerical
solution of the structure of pulsar magnetospheres, which has been an
unsolved problem for close to 40 years. Then I will consider the
magnetospheres of flaring magnetars and accretion disks, and discuss
comparison to observations and future directions.