7,165 research outputs found
Absence of Long-Range Coherence in the Parametric Emission from Photonic Wires
We analytically investigate the spatial coherence properties of the signal
emission from one-dimensional optical parametric oscillators. Because of the
reduced dimensionality, quantum fluctuations are able to destroy the long-range
phase coherence even far above threshold. The spatial decay of coherence is
exponential and, for realistic parameters of semiconductor photonic wires in
the strong exciton-photon coupling regime, it is predicted to occur on an
experimentally accessible length scale.Comment: 6 pages, 3 figure
Two-body problem in periodic potentials
We investigate the problem of two atoms interacting via a short range s-wave
potential in the presence of a deep optical lattice of arbitrary dimension .
Using a tight binding approach, we derive analytical results for the properties
of the bound state and the scattering amplitude. We show that the tunneling
through the barriers induces a dimensional crossover from a confined regime at
high energy to an anisotropic three dimensional regime at low energy. The
critical value of the scattering length needed to form a two-body bound state
shows a logaritmic dependence on the tunneling rate for D=1 and a power law for
. For the special case D=1, we also compare our analytical predictions
with exact numerics, finding remarkably good agreement
Path integral formulation of the tunneling dynamics of a superfluid Fermi gas in an optical potential
To describe the tunneling dynamics of a stack of two-dimensional fermionic
superfluids in an optical potential, we derive an effective action functional
from a path integral treatment. This effective action leads, in the saddle
point approximation, to equations of motion for the density and the phase of
the superfluid Fermi gas in each layer. In the strong coupling limit (where
bosonic molecules are formed) these equations reduce to a discrete nonlinear
Schrodinger equation, where the molecular tunneling amplitude is reduced for
large binding energies. In the weak coupling (BCS) regime, we study the
evolution of the stacked superfluids and derive an approximate analytical
expression for the Josephson oscillation frequency in an external harmonic
potential. Both in the weak and intermediate coupling regimes the detection of
the Josephson oscillations described by our path integral treatment constitutes
experimental evidence for the fermionic superfluid regime.Comment: 13 pages + 2 figure
Probing few-particle Laughlin states of photons via correlation measurements
We propose methods to create and observe Laughlin-like states of photons in a
strongly nonlinear optical cavity. Such states of strongly interacting photons
can be prepared by pumping the cavity with a Laguerre-Gauss beam, which has a
well-defined orbital angular momentum per photon. The Laughlin-like states
appear as sharp resonances in the particle-number-resolved transmission
spectrum. Power spectrum and second-order correlation function measurements
yield unambiguous signatures of these few-particle strongly-correlated states.Comment: 11 pages including appendice
Gutzwiller Monte Carlo approach for a critical dissipative spin model
We use the Gutzwiller Monte Carlo approach to simulate the dissipative
XYZ-model in the vicinity of a dissipative phase transition. This approach
captures classical spatial correlations together with the full on-site quantum
behavior, while neglecting non-local quantum effects. By considering finite
two-dimensional lattices of various sizes, we identify a ferromagnetic and two
paramagnetic phases, in agreement with earlier studies. The greatly reduced
numerical complexity the Gutzwiller Monte Carlo approach facilitates efficient
simulation of relatively large lattice sizes. The inclusion of the spatial
correlations allows to describe critical behavior which is completely missed by
the widely applied Gutzwiller decoupling of the density matrix
Correlations in Free Fermionic States
We study correlations in a bipartite, Fermionic, free state in terms of
perturbations induced by one party on the other. In particular, we show that
all so conditioned free states can be modelled by an auxiliary Fermionic system
and a suitable completely positive map.Comment: 17 pages, no figure
Predicting future reading problems based on pre-reading auditory measures: a longitudinal study of children with a familial risk of dyslexia
Purpose: This longitudinal study examines measures of temporal auditory processing
in pre-reading children with a family risk of dyslexia. Specifically, it attempts to
ascertain whether pre-reading auditory processing, speech perception, and phonological
awareness (PA) reliably predict later literacy achievement. Additionally, this study
retrospectively examines the presence of pre-reading auditory processing, speech
perception, and PA impairments in children later found to be literacy impaired.
Method: Forty-four pre-reading children with and without a family risk of dyslexia were
assessed at three time points (kindergarten, first, and second grade). Auditory processing
measures of rise time (RT) discrimination and frequency modulation (FM) along with
speech perception, PA, and various literacy tasks were assessed.
Results: Kindergarten RT uniquely contributed to growth in literacy in grades one and
two, even after controlling for letter knowledge and PA. Highly significant concurrent and
predictive correlations were observed with kindergarten RT significantly predicting first
grade PA. Retrospective analysis demonstrated atypical performance in RT and PA at all
three time points in children who later developed literacy impairments.
Conclusions: Although significant, kindergarten auditory processing contributions to
later literacy growth lack the power to be considered as a single-cause predictor; thus
results support temporal processing deficits’ contribution within a multiple deficit model
of dyslexia
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