5,066 research outputs found
Superradiance and multiple scattering of photons in atomic gases
We study the influence of cooperative effects such as superradiance and
subradiance, on the scattering properties of dilute atomic gases. We show that
cooperative effects lead to an effective potential between pairs of atoms that
decays like . In the case of superradiance, this potential is attractive
for close enough atoms and can be interpreted as a coherent mesoscopic effect.
We consider a model of multiple scattering of a photon among superradiant pairs
and calculate the elastic mean free path and the group velocity. We study first
the case of a scalar wave which allows to obtain and to understand basic
features of cooperative effects and multiple scattering. We then turn to the
general problem of a vector wave. In both cases, we obtain qualitatively
similar results and derive, for the case of a scalar wave, analytic expressions
of the elastic mean free path and of the group velocity for an arbitrary (near
resonance) detuning.Comment: 12 pages, 7 figure
Intensity correlations and mesoscopic fluctuations of diffusing photons in cold atoms
We study the angular correlation function of speckle patterns that result
from multiple scattering of photons by cold atomic clouds. We show that this
correlation function becomes larger than the value given by Rayleigh law for
classical scatterers. These large intensity fluctuations constitute a new
mesoscopic interference effect specific to atom-photon interactions, that could
not be observed in other systems such as weakly disordered metals. We provide a
complete description of this behavior and expressions that allow for a
quantitative comparison with experiments.Comment: 4 pages, 2 figure
Power Load Management as a Computational Market
Power load management enables energy utilities to reduce peak loads and thereby save money. Due to the large number of different loads, power load management is a complicated optimization problem. We present a new decentralized approach to this problem by modeling direct load management as a computational market. Our simulation results demonstrate that our approach is very efficient with a superlinear rate of convergence to equilibrium and an excellent scalability, requiring few iterations even when the number of agents is in the order of one thousand. Aframework for analysis of this and similar problems is given which shows how nonlinear optimization and numerical mathematics can be exploited to characterize, compare, and tailor problem-solving strategies in market-oriented programming
Effect of superradiance on transport of diffusing photons in cold atomic gases
We show that in atomic gases cooperative effects like superradiance and
subradiance lead to a potential between two atoms that decays like . In
the case of superradiance, this potential is attractive for close enough atoms
and can be interpreted as a coherent mesoscopic effect. The contribution of
superradiant pairs to multiple scattering properties of a dilute gas, such as
photon elastic mean free path and group velocity, is significantly different
from that of independent atoms. We discuss the conditions under which these
effects may be observed and compare our results to recent experiments on photon
transport in cold atomic gases.Comment: 4 pages and 1 figur
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