3,426 research outputs found
An Isotropic to Anisotropic Transition in a Fractional Quantum Hall State
We study a novel abelian gauge theory in 2+1 dimensions which has surprising
theoretical and phenomenological features. The theory has a vanishing
coefficient for the square of the electric field , characteristic of a
quantum critical point with dynamical critical exponent , and a level-
Chern-Simons coupling, which is {\it marginal} at this critical point. For
, this theory is dual to a free scalar field theory describing a
quantum Lifshitz transition, but renders the scalar description
non-local. The theory exhibits properties intermediate between the
(topological) pure Chern-Simons theory and the scalar theory. For instance, the
Chern-Simons term does not make the gauge field massive. Nevertheless, there
are chiral edge modes when the theory is placed on a space with boundary, and a
non-trivial ground state degeneracy when it is placed on a finite-size
Riemann surface of genus . The coefficient of is the only relevant
coupling; it tunes the system through a quantum phase transition between an
isotropic fractional quantum Hall state and an anisotropic fractional quantum
Hall state. We compute zero-temperature transport coefficients in both phases
and at the critical point, and comment briefly on the relevance of our results
to recent experiments.Comment: 29 pages, 1 figur
Tilted Interferometry Realizes Universal Quantum Computation in the Ising TQFT without Overpasses
We show how a universal gate set for topological quantum computation in the
Ising TQFT, the non-Abelian sector of the putative effective field theory of
the fractional quantum Hall state, can be implemented. This
implementation does not require overpasses or surgery, unlike the construction
of Bravyi and Kitaev, which we take as a starting point. However, it requires
measurements of the topological charge around time-like loops encircling moving
quasiaparticles, which require the ability to perform `tilted' interferometry
measurements.Comment: This manuscript has substantial overlap with cond-mat/0512066 which
contains more physics and less emphasis on the topology. The present
manuscript is posted as a possibly useful companion to the forme
Screening and antiscreening in anisotropic QED and QCD plasmas
We use a transport-theory approach to construct the static propagator of a
gauge boson in a plasma with a general axially- and reflection-symmetric
momentum distribution. Non-zero magnetic screening is found if the distribution
is anisotropic, confirming the results of a closed-time-path-integral approach.
We find that the electric and magnetic screening effects depend on both the
orientation of the momentum carried by the boson and the orientation of its
polarization. In some orientations there can be antiscreening, reflecting the
instabilities of such a medium. We present some fairly general conditions on
the dependence of these effects on the anisotropy.Comment: 14 pages late
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