26 research outputs found
Rejoinder on "Conjectures on exact solution of three-dimensional (3D) simple orthorhombic Ising lattices"
It is shown that the arguments in the reply of Z.-D. Zhang (arXiv:0812.0194)
to the comment arXiv:0811.1802 defending his conjectures in arXiv:0705.1045 are
invalid. His conjectures have been thoroughly disproved.Comment: LaTeX2e, 2 pages, added responses to arXiv:0812.0194v3 and
arXiv:0812.0194v
Nonequilibrium Forces Between Neutral Atoms Mediated by a Quantum Field
We study all known and as yet unknown forces between two neutral atoms,
modeled as three dimensional harmonic oscillators, arising from mutual
influences mediated by an electromagnetic field but not from their direct
interactions. We allow as dynamical variables the center of mass motion of the
atom, its internal degrees of freedom and the quantum field treated
relativistically. We adopt the method of nonequilibrium quantum field theory
which can provide a first principle, systematic and unified description
including the intrinsic field fluctuations and induced dipole fluctuations. The
inclusion of self-consistent back-actions makes possible a fully dynamical
description of these forces valid for general atom motion. In thermal
equilibrium we recover the known forces -- London, van der Waals and
Casimir-Polder forces -- between neutral atoms in the long-time limit but also
discover the existence of two new types of interatomic forces. The first, a
`nonequilibrium force', arises when the field and atoms are not in thermal
equilibrium, and the second, which we call an `entanglement force', originates
from the correlations of the internal degrees of freedom of entangled atoms.Comment: 16 pages, 2 figure
Dynamics and transport near quantum-critical points
The physics of non-zero temperature dynamics and transport near
quantum-critical points is discussed by a detailed study of the O(N)-symmetric,
relativistic, quantum field theory of a N-component scalar field in spatial
dimensions. A great deal of insight is gained from a simple, exact solution of
the long-time dynamics for the N=1 d=1 case: this model describes the critical
point of the Ising chain in a transverse field, and the dynamics in all the
distinct, limiting, physical regions of its finite temperature phase diagram is
obtained. The N=3, d=1 model describes insulating, gapped, spin chain
compounds: the exact, low temperature value of the spin diffusivity is
computed, and compared with NMR experiments. The N=3, d=2,3 models describe
Heisenberg antiferromagnets with collinear N\'{e}el correlations, and
experimental realizations of quantum-critical behavior in these systems are
discussed. Finally, the N=2, d=2 model describes the superfluid-insulator
transition in lattice boson systems: the frequency and temperature dependence
of the the conductivity at the quantum-critical coupling is described and
implications for experiments in two-dimensional thin films and inversion layers
are noted.Comment: Lectures presented at the NATO Advanced Study Institute on "Dynamical
properties of unconventional magnetic systems", Geilo, Norway, April 2-12,
1997, edited by A. Skjeltorp and D. Sherrington, Kluwer Academic, to be
published. 46 page
Ultracold atomic gases in optical lattices: mimicking condensed matter physics and beyond
We review recent developments in the physics of ultracold atomic and
molecular gases in optical lattices. Such systems are nearly perfect
realisations of various kinds of Hubbard models, and as such may very well
serve to mimic condensed matter phenomena. We show how these systems may be
employed as quantum simulators to answer some challenging open questions of
condensed matter, and even high energy physics. After a short presentation of
the models and the methods of treatment of such systems, we discuss in detail,
which challenges of condensed matter physics can be addressed with (i)
disordered ultracold lattice gases, (ii) frustrated ultracold gases, (iii)
spinor lattice gases, (iv) lattice gases in "artificial" magnetic fields, and,
last but not least, (v) quantum information processing in lattice gases. For
completeness, also some recent progress related to the above topics with
trapped cold gases will be discussed.Comment: Review article. v2: published version, 135 pages, 34 figure