10 research outputs found
Beyond Gross-Pitaevskii Mean Field Theory
A large number of effects related to the phenomenon of Bose-Einstein
Condensation (BEC) can be understood in terms of lowest order mean field
theory, whereby the entire system is assumed to be condensed, with thermal and
quantum fluctuations completely ignored. Such a treatment leads to the
Gross-Pitaevskii Equation (GPE) used extensively throughout this book. Although
this theory works remarkably well for a broad range of experimental parameters,
a more complete treatment is required for understanding various experiments,
including experiments with solitons and vortices. Such treatments should
include the dynamical coupling of the condensate to the thermal cloud, the
effect of dimensionality, the role of quantum fluctuations, and should also
describe the critical regime, including the process of condensate formation.
The aim of this Chapter is to give a brief but insightful overview of various
recent theories, which extend beyond the GPE. To keep the discussion brief,
only the main notions and conclusions will be presented. This Chapter
generalizes the presentation of Chapter 1, by explicitly maintaining
fluctuations around the condensate order parameter. While the theoretical
arguments outlined here are generic, the emphasis is on approaches suitable for
describing single weakly-interacting atomic Bose gases in harmonic traps.
Interesting effects arising when condensates are trapped in double-well
potentials and optical lattices, as well as the cases of spinor condensates,
and atomic-molecular coupling, along with the modified or alternative theories
needed to describe them, will not be covered here.Comment: Review Article (19 Pages) - To appear in 'Emergent Nonlinear
Phenomena in Bose-Einstein Condensates: Theory and Experiment', Edited by
P.G. Kevrekidis, D.J. Frantzeskakis and R. Carretero-Gonzalez (Springer
Verlag
Possible nematic to smectic phase transition in a two-dimensional electron gas at half-filling
Finite particle size drives defect-mediated domain structures in strongly confined colloidal liquid crystals
Laser spectroscopic characterization of the nuclear-clock isomer Th
The isotope Th is the only nucleus known to possess an excited state
Th in the energy range of a few electron volts, a transition energy
typical for electrons in the valence shell of atoms, but about four orders of
magnitude lower than common nuclear excitation energies. A number of
applications of this unique nuclear system, which is accessible by optical
methods, have been proposed. Most promising among them appears a highly precise
nuclear clock that outperforms existing atomic timekeepers. Here we present the
laser spectroscopic investigation of the hyperfine structure of
Th, yielding values of fundamental nuclear properties, namely
the magnetic dipole and electric quadrupole moments as well as the nuclear
charge radius. After the recent direct detection of this long-searched-for
isomer, our results now provide detailed insight into its nuclear structure and
present a method for its non-destructive optical detection.Comment: 18 page