97 research outputs found
Three-point density correlation functions in the fractional quantum Hall regime
In this paper we consider the three-particle density correlation function for
a fractional quantum Hall liquid. The study of this object is motivated by
recent experimental studies of fractional quantum Hall systems using inelastic
light scattering and phonon absorption techniques. Symmetry properties of the
correlation function are noted. An exact sum-rule is derived which this
quantity must obey. This sum-rule is used to assess the convolution
approximation that has been used to estimate the matrix elements for such
experiments. PACS Numbers: 73.40.Hm, 73.20.Mf, 72.10.DiComment: 12 pages + 1 (PS) figur
On the feasibility of studying vortex noise in 2D superconductors with cold atoms
We investigate the feasibility of using ultracold neutral atoms trapped near
a thin superconductor to study vortex noise close to the
Kosterlitz-Thouless-Berezinskii transition temperature. Alkali atoms such as
rubidium probe the magnetic field produced by the vortices. We show that the
relaxation time of the Zeeman sublevel populations can be conveniently
adjusted to provide long observation times. We also show that the transverse
relaxation times for Zeeman coherences are ideal for studying the vortex
noise. We briefly consider the motion of atom clouds held close to the surface
as a method for monitoring the vortex motion.Comment: 4 pages, 1 figur
Accurate statistics of a flexible polymer chain in shear flow
We present exact and analytically accurate results for the problem of a
flexible polymer chain in shear flow. Under such a flow the polymer tumbles,
and the probability distribution of the tumbling times of the polymer
decays exponentially as (where is the
longest relaxation time). We show that for a Rouse chain, this nontrivial
constant can be calculated in the limit of large Weissenberg number
(high shear rate) and is in excellent agreement with our simulation result of
. We also derive exactly the distribution functions for
the length and the orientational angles of the end-to-end vector of the
polymer.Comment: 4 pages, 2 figures. Minor changes. Texts differ slightly from the PRL
published versio
Classical diffusion of N interacting particles in one dimension: General results and asymptotic laws
I consider the coupled one-dimensional diffusion of a cluster of N classical
particles with contact repulsion. General expressions are given for the
probability distributions, allowing to obtain the transport coefficients. In
the limit of large N, and within a gaussian approximation, the diffusion
constant is found to behave as N^{-1} for the central particle and as (\ln
N)^{-1} for the edge ones. Absolute correlations between the edge particles
increase as (\ln N)^{2}. The asymptotic one-body distribution is obtained and
discussed in relation of the statistics of extreme events.Comment: 6 pages, 2 eps figure
Dephasing by a nonstationary classical intermittent noise
We consider a new phenomenological model for a classical
intermittent noise and study its effects on the dephasing of a two-level
system. Within this model, the evolution of the relative phase between the
states is described as a continuous time random walk (CTRW). Using
renewal theory, we find exact expressions for the dephasing factor and identify
the physically relevant various regimes in terms of the coupling to the noise.
In particular, we point out the consequences of the non-stationarity and
pronounced non-Gaussian features of this noise, including some new anomalous
and aging dephasing scenarii.Comment: Submitted to Phys. Rev.
Dressed-State Approach to Population Trapping in the Jaynes-Cummings Model
The phenomenon of atomic population trapping in the Jaynes-Cummings Model is
analysed from a dressed-state point of view. A general condition for the
occurrence of partial or total trapping from an arbitrary, pure initial
atom-field state is obtained in the form of a bound to the variation of the
atomic inversion. More generally, it is found that in the presence of initial
atomic or atom-field coherence the population dynamics is governed not by the
field's initial photon distribution, but by a `weighted dressedness'
distribution characterising the joint atom-field state. In particular,
individual revivals in the inversion can be analytically described to good
approximation in terms of that distribution, even in the limit of large
population trapping. This result is obtained through a generalisation of the
Poisson Summation Formula method for analytical description of revivals
developed by Fleischhauer and Schleich [Phys. Rev. A {\bf 47}, 4258 (1993)].Comment: 24 pages, 5 figures, to appear in J. Mod. Op
Broad-tailed force distributions and velocity ordering in a heterogeneous membrane model for collective cell migration
Correlated velocity patterns and associated large length-scale transmission
of traction forces have been observed in collective live cell migration as a
response to a "wound". We argue that a simple physical model of a force-driven
heterogeneous elastic membrane sliding over a viscous substrate can
qualitatively explain a few experimentally observed facts: (i) the growth of
velocity ordering which spreads from the wound boundary to the interior, (ii)
the exponential tails of the traction force distributions, and (iii) the
swirling pattern of velocities in the interior of the tissue.Comment: 7 pages and 5 figure
Analytic calculation of energies and wave functions of the quartic and pure quartic oscillators
Ground state energies and wave functions of quartic and pure quartic
oscillators are calculated by first casting the Schr\"{o}dinger equation into a
nonlinear Riccati form and then solving that nonlinear equation analytically in
the first iteration of the quasilinearization method (QLM). In the QLM the
nonlinear differential equation is solved by approximating the nonlinear terms
by a sequence of linear expressions. The QLM is iterative but not perturbative
and gives stable solutions to nonlinear problems without depending on the
existence of a smallness parameter. Our explicit analytic results are then
compared with exact numerical and also with WKB solutions and it is found that
our ground state wave functions, using a range of small to large coupling
constants, yield a precision of between 0.1 and 1 percent and are more accurate
than WKB solutions by two to three orders of magnitude. In addition, our QLM
wave functions are devoid of unphysical turning point singularities and thus
allow one to make analytical estimates of how variation of the oscillator
parameters affects physical systems that can be described by the quartic and
pure quartic oscillators.Comment: 8 pages, 12 figures, 1 tabl
Hamiltonian solutions of the 3-body problem in (2+1)-gravity
We present a full study of the 3-body problem in gravity in flat
(2+1)-dimensional space-time, and in the nonrelativistic limit of small
velocities. We provide an explicit form of the ADM Hamiltonian in a regular
coordinate system and we set up all the ingredients for canonical quantization.
We emphasize the role of a U(2) symmetry under which the Hamiltonian is
invariant and which should generalize to a U(N-1) symmetry for N bodies. This
symmetry seems to stem from a braid group structure in the operations of
looping of particles around each other, and guarantees the single-valuedness of
the Hamiltonian. Its role for the construction of single-valued energy
eigenfunctions is also discussed.Comment: 25 pages, no figure. v2: some calculation details removed to make the
paper more concise (see v1 for the longer version), minor correction in a
formula in the section on quantization, references added; results and
conclusions unchange
Upper bounds on success probabilities in linear optics
We develop an abstract way of defining linear-optics networks designed to
perform quantum information tasks such as quantum gates. We will be mainly
concerned with the nonlinear sign shift gate, but it will become obvious that
all other gates can be treated in a similar manner. The abstract scheme is
extremely well suited for analytical as well as numerical investigations since
it reduces the number of parameters for a general setting. With that we show
numerically and partially analytically for a wide class of states that the
success probability of generating a nonlinear sign shift gate does not exceed
1/4 which to our knowledge is the strongest bound to date.Comment: 8 pages, typeset using RevTex4, 5 EPS figure
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