584 research outputs found
Vortices Clustering: The Origin of the Second Peak in the Magnetisation Loops of High Temperature Superconductors
We study vortex clustering in type II Superconductors. We demonstrate that
the ``second peak'' observed in magnetisation loops may be a dynamical effect
associated with a density driven instability of the vortex system. At the
microscopic level the instability shows up as the clustering of individual
vortices at (rare) preferential regions of the pinning potential. In the limit
of quasi-static ramping the instability is related to a phase transition in the
equilibrium vortex system.Comment: 11 pages + 3 figure
Meanfield treatment of Bragg scattering from a Bose-Einstein condensate
A unified semiclassical treatment of Bragg scattering from Bose-Einstein
condensates is presented. The formalism is based on the Gross-Pitaevskii
equation driven by classical light fields far detuned from atomic resonance. An
approximate analytic solution is obtained and provides quantitative
understanding of the atomic momentum state oscillations, as well as a simple
expression for the momentum linewidth of the scattering process. The validity
regime of the analytic solution is derived, and tested by three dimensional
cylindrically symmetric numerical simulations.Comment: 21 pages, 10 figures. Minor changes made to documen
Intellectual Property Rights in Digital Media: A Comparative Analysis of Legal Protection, Technological Measures and New Business Models under E.U. and U.S. Law
Lattice supersymmetry, superfields and renormalization
We study Euclidean lattice formulations of non-gauge supersymmetric models
with up to four supercharges in various dimensions. We formulate the conditions
under which the interacting lattice theory can exactly preserve one or more
nilpotent anticommuting supersymmetries. We introduce a superfield formalism,
which allows the enumeration of all possible lattice supersymmetry invariants.
We use it to discuss the formulation of Q-exact lattice actions and their
renormalization in a general manner. In some examples, one exact supersymmetry
guarantees finiteness of the continuum limit of the lattice theory. As a
consequence, we show that the desired quantum continuum limit is obtained
without fine tuning for these models. Finally, we discuss the implications and
possible further applications of our results to the study of gauge and
non-gauge models.Comment: 44 pages, 1 figur
Enhanced absorption Hanle effect on the Fg=F->Fe=F+1 closed transitions
We analyse the Hanle effect on a closed transition. Two
configurations are examined, for linear- and circular-polarized laser
radiation, with the applied magnetic field collinear to the laser light
wavevector. We describe the peculiarities of the Hanle signal for
linearly-polarized laser excitation, characterized by narrow bright resonances
at low laser intensities. The mechanism behind this effect is identified, and
numerical solutions for the optical Bloch equations are presented for different
transitions.Comment: to be published in J. Opt. B, special issue on Quantum Coherence and
Entanglement (February 2001
Ground state cooling in a bad cavity
We study the mechanical effects of light on an atom trapped in a harmonic
potential when an atomic dipole transition is driven by a laser and it is
strongly coupled to a mode of an optical resonator. We investigate the cooling
dynamics in the bad cavity limit, focussing on the case in which the effective
transition linewidth is smaller than the trap frequency, hence when sideband
cooling could be implemented. We show that quantum correlations between the
mechanical actions of laser and cavity field can lead to an enhancement of the
cooling efficiency with respect to sideband cooling. Such interference effects
are found when the resonator losses prevail over spontaneous decay and over the
rates of the coherent processes characterizing the dynamics.Comment: 6 pages, 5 figures; J. Mod. Opt. (2007
- …