165 research outputs found
Phase transitions with finite atom number in the Dicke Model
Two-level atoms interacting with a one mode cavity field at zero temperature
have order parameters which reflect the presence of a quantum phase transition
at a critical value of the atom-cavity coupling strength. Two popular examples
are the number of photons inside the cavity and the number of excited atoms.
Coherent states provide a mean field description, which becomes exact in the
thermodynamic limit. Employing symmetry adapted (SA) SU(2) coherent states
(SACS) the critical behavior can be described for a finite number of atoms. A
variation after projection treatment, involving a numerical minimization of the
SA energy surface, associates the finite number phase transition with a
discontinuity in the order parameters, which originates from a competition
between two local minima in the SA energy surface.Comment: 8 pages, 10 figures, Conference Proceedings of CEWQO-2012, to be
published as a Topical Issue of the journal Physica Script
Searching for pairing energies in phase space
We obtain a representation of pairing energies in phase space, for the
Lipkin-Meshkov-Glick and general boson Bardeen-Cooper-Schrieffer pairing
models. This is done by means of a probability distribution of the quantum
state in phase space. In fact, we prove a correspondence between the points at
which this probability distribution vanishes and the pairing energies. In
principle, the vanishing of this probability distribution is experimentally
accessible and additionally gives a method to visualize pairing energies across
the model control parameter space. This result opens new ways to experimentally
approach quantum pairing systems.Comment: 5 pages, 4 figure
Linear Time-Dependent Invariants for Scalar Fields and Noether's Theorem
The infinite number of time-dependent linear in field and conjugated momenta
invariants is derived for the scalar field using the Noether's theorem
procedure.Comment: LaTeX, 6 pages, preprint of Instituto de Ciencias Nucleares, UNAM,
Departamento de F\ii sica and Matem\'aticas Aplicadas, M\'exico D. F. ,
M\'exico No. 04 (1994
Squeezing in a 2-D generalized oscillator
A two-dimensional generalized oscillator with time-dependent parameters is
considered to study the two-mode squeezing phenomena. Specific choices of the
parameters are used to determine the dispersion matrix and analytic
expressions, in terms of standard hermite polynomials, of the wavefunctions and
photon distributions. (to be publish in the Third Workshop on Squeezed States
and Uncertainty Relations, Baltimore, USA, (August 1993))Comment: LaTeX, 5 pages, preprint of Instituto de Ciencias Nucleares, UNAM
Departamento de F\ii sica and Matem\'aticas Aplicadas, No. 02 (1994
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