16,069 research outputs found
Correlations and fluctuations of a confined electron gas
The grand potential and the response of a phase-coherent confined noninteracting electron gas depend
sensitively on chemical potential or external parameter . We compute
their autocorrelation as a function of , and temperature. The result
is related to the short-time dynamics of the corresponding classical system,
implying in general the absence of a universal regime. Chaotic, diffusive and
integrable motions are investigated, and illustrated numerically. The
autocorrelation of the persistent current of a disordered mesoscopic ring is
also computed.Comment: 12 pages, 1 figure, to appear in Phys. Rev.
Localization of Electromagnetic Fields in Disordered Fano Metamaterials
We present the first study of disorder in planar metamaterials consisting of
strongly interacting metamolecules, where coupled electric dipole and magnetic
dipole modes give rise to a Fano-type resonant response and show that
positional disorder leads to light localization inherently linked to collective
magnetic dipole excitations. We demonstrate that the magnetic excitation
persists in disordered arrays and results in the formation of "magnetic
hot-spots"
Construction of localized wave functions for a disordered optical lattice and analysis of the resulting Hubbard model parameters
We propose a method to construct localized single particle wave functions
using imaginary time projection and thereby determine lattice Hamiltonian
parameters. We apply the method to a specific disordered potential generated by
an optical lattice experiment and calculate for each instance of disorder, the
equivalent lattice model parameters. The probability distributions of the
Hubbard parameters are then determined. Tests of localization and eigen-energy
convergence are examined.Comment: 10 pages, 16 figure
Model-independent measurements of the sodium magneto-optical trap's excited-state population
We present model-independent measurements of the excited-state population of
atoms in a sodium (Na) magneto-optical trap (MOT) using a hybrid ion-neutral
trap composed of a MOT and a linear Paul trap (LPT). We photoionize excited Na
atoms trapped in the MOT and use two independent methods to measure the
resulting ions: directly by trapping them in our LPT, and indirectly by
monitoring changes in MOT fluorescence. By measuring the ionization rate via
these two independent methods, we have enough information to directly determine
the population of MOT atoms in the excited-state. The resulting measurement
reveals that there is a range of trapping-laser intensities where the
excited-state population of atoms in our MOT follows the standard two-level
model intensity-dependence. However, an experimentally determined effective
saturation intensity must be used instead of the theoretically predicted value
from the two-level model. We measured the effective saturation intensity to be
for the type-I Na MOT and
for the type-II Na MOT,
approximately 1.7 and 3.6 times the theoretical estimate, respectively. Lastly,
at large trapping-laser intensities, our experiment reveals a clear departure
from the two-level model at a critical intensity that we believe is due to a
state-mixing effect, whose critical intensity can be determined by a simple
power broadening model.Comment: 10 pages, 8 figure
Evidence of sympathetic cooling of Na+ ions by a Na MOT in a hybrid trap
A hybrid ion-neutral trap provides an ideal system to study collisional
dynamics between ions and neutrals. This system provides a general cooling
method that can be applied to optically inaccessible species and can also
potentially cool internal degrees of freedom. The long range polarization
potentials () between ions and neutrals result in large
scattering cross sections at cold temperatures, making the hybrid trap a
favorable system for efficient sympathetic cooling of ions by collisions with
neutral atoms. We present experimental evidence of sympathetic cooling in a
hybrid trap of \ce{Na+} ions, which are closed shell and therefore do not have
a laser induced atomic transition, by equal mass cold Na atoms in a
magneto-optical trap (MOT).Comment: 7 figure
Ion-neutral sympathetic cooling in a hybrid linear rf Paul and magneto-optical trap
Long range polarization forces between ions and neutral atoms result in large
elastic scattering cross sections, e.g., 10^6 a.u. for Na+ on Na or Ca+ on Na
at cold and ultracold temperatures. This suggests that a hybrid ion-neutral
trap should offer a general means for significant sympathetic cooling of atomic
or molecular ions. We present SIMION 7.0 simulation results concerning the
advantages and limitations of sympathetic cooling within a hybrid trap
apparatus, consisting of a linear rf Paul trap concentric with a Na
magneto-optical trap (MOT). This paper explores the impact of various heating
mechanisms on the hybrid system and how parameters related to the MOT, Paul
trap, number of ions, and ion species affect the efficiency of the sympathetic
cooling
Giant fluctuations of topological charge in a disordered wave guide
We study the fluctuations of the total topological charge of a scalar wave
propagating in a hollow conducting wave guide filled with scatterers inside. We
investigate the dependence of the screening on the scattering mean free path
and on the presence of boundaries. Near the cut-off frequencies of the wave
guide, screening is strongly suppressed near the boundaries. The resulting huge
fluctuations of the total topological charge are very sensitive to the
disorder.Comment: 8 pages 5 figures, submitted to Waves in Random and Complex Medi
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