206 research outputs found
Probability Distributions and Hilbert Spaces: Quantum and Classical Systems
We use the fact that some linear Hamiltonian systems can be considered as
``finite level'' quantum systems, and the description of quantum mechanics in
terms of probabilities, to associate probability distributions with this
particular class of linear Hamiltonian systems.Comment: LATEX,13pages,accepted by Physica Scripta (1999
Radon transform on the cylinder and tomography of a particle on the circle
The tomographic probability distribution on the phase space (cylinder)
related to a circle or an interval is introduced. The explicit relations of the
tomographic probability densities and the probability densities on the phase
space for the particle motion on a torus are obtained and the relation of the
suggested map to the Radon transform on the plane is elucidated. The
generalization to the case of a multidimensional torus is elaborated and the
geometrical meaning of the tomographic probability densities as marginal
distributions on the helix discussed.Comment: 9 pages, 3 figure
Classical and Quantum Systems: Alternative Hamiltonian Descriptions
In complete analogy with the classical situation (which is briefly reviewed)
it is possible to define bi-Hamiltonian descriptions for Quantum systems. We
also analyze compatible Hermitian structures in full analogy with compatible
Poisson structures.Comment: To appear on Theor. Math. Phy
Towards a definition of quantum integrability
We briefly review the most relevant aspects of complete integrability for
classical systems and identify those aspects which should be present in a
definition of quantum integrability.
We show that a naive extension of classical concepts to the quantum framework
would not work because all infinite dimensional Hilbert spaces are unitarily
isomorphic and, as a consequence, it would not be easy to define degrees of
freedom. We argue that a geometrical formulation of quantum mechanics might
provide a way out.Comment: 37 pages, AmsLatex, 1 figur
Classical Tensors and Quantum Entanglement II: Mixed States
Invariant operator-valued tensor fields on Lie groups are considered. These
define classical tensor fields on Lie groups by evaluating them on a quantum
state. This particular construction, applied on the local unitary group
U(n)xU(n), may establish a method for the identification of entanglement
monotone candidates by deriving invariant functions from tensors being by
construction invariant under local unitary transformations. In particular, for
n=2, we recover the purity and a concurrence related function (Wootters 1998)
as a sum of inner products of symmetric and anti-symmetric parts of the
considered tensor fields. Moreover, we identify a distinguished entanglement
monotone candidate by using a non-linear realization of the Lie algebra of
SU(2)xSU(2). The functional dependence between the latter quantity and the
concurrence is illustrated for a subclass of mixed states parametrized by two
variables.Comment: 23 pages, 4 figure
Trapped Ions in Laser Fields: a Benchmark for Deformed-Quantum Oscillators
Some properties of the non--linear coherent states (NCS), recognized by Vogel and de Matos Filho as dark states of a trapped ion, are extended to NCS on a circle, for which the Wigner functions are presented. These states are obtained by applying a suitable displacement operator to the vacuum state. The unity resolutions in terms of the projectors . is also used for introducing the probability distribution funtion while the existence of a measure is exploited for extending the P-representation to these states. The weight of the n-th Fock state of the NCS relative to a trapped ion with Lamb-Dicke parameter oscillates so wildly as grows up to infinity that the normalized NCS fill the open circle in the complex -plane. In addition this prevents the existence of a measure including normalizable states only. This difficulty is overcome by introducing a family of deformations which are rational functions of n, each of them admitting a measure. By increasing the degree of these rational approximations the deformation of a trapped ion can be approximated with any degree of accuracy and the formalism of the P-representation can be applied
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