9,254 research outputs found
Multiply-connected Bose-Einstein condensed alkali gases: Current-carrying states and their decay
The ability to support metastable current-carrying states in
multiply-connected settings is one of the prime signatures of superfluidity.
Such states are investigated theoretically for the case of trapped Bose
condensed alkali gases, particularly with regard to the rate at which they
decay via thermal fluctuations. The lifetimes of metastable currents can be
either longer or shorter than experimental time-scales. A scheme for the
experimental detection of metastable states is sketched.Comment: 4 pages, including 1 figure (REVTEX
Experimental demonstration of a technique to generate arbitrary quantum superposition states
Using a single, harmonically trapped Be ion, we experimentally
demonstrate a technique for generation of arbitrary states of a two-level
particle confined by a harmonic potential. Rather than engineering a single
Hamiltonian that evolves the system to a desired final sate, we implement a
technique that applies a sequence of simple operations to synthesize the state
Quantum information processing with trapped ions
Experiments directed towards the development of a quantum computer based on
trapped atomic ions are described briefly. We discuss the implementation of
single qubit operations and gates between qubits. A geometric phase gate
between two ion qubits is described. Limitations of the trapped-ion method such
as those caused by Stark shifts and spontaneous emission are addressed.
Finally, we describe a strategy to realize a large-scale device.Comment: Article submitted by D. J. Wineland ([email protected])
for proceeding of the Discussion Meeting on Practical Realisations of Quantum
Information Processing, held at the Royal Society, Nov. 13,14, 200
Competitive nucleation in reversible Probabilistic Cellular Automata
The problem of competitive nucleation in the framework of Probabilistic
Cellular Automata is studied from the dynamical point of view. The dependence
of the metastability scenario on the self--interaction is discussed. An
intermediate metastable phase, made of two flip--flopping chessboard
configurations, shows up depending on the ratio between the magnetic field and
the self--interaction. A behavior similar to the one of the stochastic
Blume--Capel model with Glauber dynamics is found
Theory for Dynamical Short Range Order and Fermi Surface Volume in Strongly Correlated Systems
Using the fluctuation exchange approximation of the one band Hubbard model,
we discuss the origin of the changing Fermi surface volume in underdoped
cuprate systems due to the transfer of occupied states from the Fermi surface
to its shadow, resulting from the strong dynamical antiferromagnetic short
range correlations. The momentum and temperature dependence of the quasi
particle scattering rate shows unusual deviations from the conventional Fermi
liquid like behavior. Their consequences for the changing Fermi surface volume
are discussed. Here, we investigate in detail which scattering processes
might be responsible for a violation of the Luttinger theorem. Finally, we
discuss the formation of hole pockets near half filling.Comment: 5 pages, Revtex, 4 postscript figure
Langevin Equation for the Density of a System of Interacting Langevin Processes
We present a simple derivation of the stochastic equation obeyed by the
density function for a system of Langevin processes interacting via a pairwise
potential. The resulting equation is considerably different from the
phenomenological equations usually used to describe the dynamics of non
conserved (Model A) and conserved (Model B) particle systems. The major feature
is that the spatial white noise for this system appears not additively but
multiplicatively. This simply expresses the fact that the density cannot
fluctuate in regions devoid of particles. The steady state for the density
function may however still be recovered formally as a functional integral over
the coursed grained free energy of the system as in Models A and B.Comment: 6 pages, latex, no figure
Elastic forces that do no work and the dynamics of fast cracks
Elastic singularities such as crack tips, when in motion through a medium
that is itself vibrating, are subject to forces orthogonal to the direction of
motion and thus impossible to determine by energy considerations alone. This
fact is used to propose a universal scenario, in which three dimensionality is
essential, for the dynamic instability of fast cracks in thin brittle
materials.Comment: 8 pages Latex, 1 Postscript figur
Thermal Phase Mixing During First Order Phase Transitions
The dynamics of first order phase transitions are studied in the context of
(3+1)-dimensional scalar field theories. Particular attention is paid to the
question of quantifying the strength of the transition, and how `weak' and
`strong' transitions have different dynamics. We propose a model with two
available low temperature phases separated by an energy barrier so that one of
them becomes metastable below the critical temperature . The system is
initially prepared in this phase and is coupled to a thermal bath.
Investigating the system at its critical temperature, we find that `strong'
transitions are characterized by the system remaining localized within its
initial phase, while `weak' transitions are characterized by considerable phase
mixing. Always at , we argue that the two regimes are themselves separated
by a (second order) phase transition, with an order parameter given by the
fractional population difference between the two phases and a control parameter
given by the strength of the scalar field's quartic self-coupling constant. We
obtain a Ginzburg-like criterion to distinguish between `weak' and `strong'
transitions, in agreement with previous results in (2+1)-dimensions.Comment: 28 pages RevTeX, 9 postscript figures, IMPERIAL/TP/93-94/58,
DART-HEP-94/0
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