2,138 research outputs found
A Generalized Jaynes-Cummings Model: Nonlinear dynamical superalgebra and Supercoherent states
The generalization of the Jaynes-Cummings (GJC) Model is proposed. In this
model, the electromagnetic radiation is described by a Hamiltonian generalizing
the harmonic oscillator to take into account some nonlinear effects which can
occurs in the experimental situations. The dynamical superalgebra and
supercoherent states of the related model are explicitly constructed. A
relevant quantities (total number of particles, energy and atomic inversion)
are computed.Comment: 12 page
On -Deformations in Statistical Mechanics of Bosons in D Dimensions
The Bose distribution for a gas of nonrelativistic free bosons is derived in
the framework of -deformed second quantization. Some thermodynamical
functions for such a system in D dimensions are derived. Bose-Einstein
condensation is discussed in terms of the parameters q and p as well as a
parameter which characterizes the representation space of the
oscillator algebra.Comment: 15 pages, Latex File, to be published in Symmetry and Structural
Properties of Condensed Matter, Eds. T. Lulek, B. Lulek and W. Florek (World
Scientific, Singapore, 1997
Phase operators, temporally stable phase states, mutually unbiased bases and exactly solvable quantum systems
We introduce a one-parameter generalized oscillator algebra A(k) (that covers
the case of the harmonic oscillator algebra) and discuss its finite- and
infinite-dimensional representations according to the sign of the parameter k.
We define an (Hamiltonian) operator associated with A(k) and examine the
degeneracies of its spectrum. For the finite (when k < 0) and the infinite
(when k > 0 or = 0) representations of A(k), we construct the associated phase
operators and build temporally stable phase states as eigenstates of the phase
operators. To overcome the difficulties related to the phase operator in the
infinite-dimensional case and to avoid the degeneracy problem for the
finite-dimensional case, we introduce a truncation procedure which generalizes
the one used by Pegg and Barnett for the harmonic oscillator. This yields a
truncated generalized oscillator algebra A(k,s), where s denotes the truncation
order. We construct two types of temporally stable states for A(k,s) (as
eigenstates of a phase operator and as eigenstates of a polynomial in the
generators of A(k,s)). Two applications are considered in this article. The
first concerns physical realizations of A(k) and A(k,s) in the context of
one-dimensional quantum systems with finite (Morse system) or infinite
(Poeschl-Teller system) discrete spectra. The second deals with mutually
unbiased bases used in quantum information.Comment: Accepted for publication in Journal of Physics A: Mathematical and
Theoretical as a pape
Two-Photon Spectroscopy Between States of Opposite Parities
Magnetic- and electric-dipole two-photon absorption (MED-TPA), recently
introduced as a new spectroscopic technique for studying transitions between
states of opposite parities, is investigated from a theoretical point of view.
A new approximation, referred to as {\it weak quasi-closure approximation}, is
used together with symmetry adaptation techniques to calculate the transition
amplitude between states having well-defined symmetry properties. Selection
rules for MED-TPA are derived and compared to selection rules for
parity-forbidden electric-dipole two-photon absorption (ED-TPA).Comment: 7 pages, Revtex File, to be published in Physical Review
Incommensurate magnetic ordering in (X=Cl,Br) studied by neutron diffraction
We present the results of the first neutron powder and single crystal
diffraction studies of the coupled spin tetrahedra systems {\CuTeX} (X=Cl,
Br). Incommensurate antiferromagnetic order with the propagation vectors
{\bf{k}_{Cl}}\approx[0.150,0.422,\half],
{\bf{k}_{Br}}\approx[0.158,0.354,\half] sets in below =18 K for X=Cl
and 11 K for X=Br. No simple collinear antiferromagnetic or ferromagnetic
arrangements of moments within Cu tetrahedra fit these observations.
Fitting the diffraction data to more complex but physically reasonable models
with multiple helices leads to a moment of 0.67(1)/Cu at 1.5 K
for the Cl-compound. The reason for such a complex ground state may be
geometrical frustration of the spins due to the intra- and inter-tetrahedral
couplings having similar strengths. The magnetic moment in the Br- compound,
calculated assuming it has the same magnetic structure as the Cl compound, is
only 0.51(5)/Cu at 1.5 K. In neither compound has any evidence
for a structural transition accompanying the magnetic ordering been found
Aggregation number distributions and mesoglobules in dilute solutions of diblock and triblock copolymers
We investigate the aggregation number and size distributions for
inter-molecular clusters of amphiphilic diblock and triblock copolymers in poor
solvent at very low concentrations. Diblocks and triblocks with hydrophilic
ends are shown to possess narrow distributions corresponding to formation of
monodispersed mesoglobules. Diblocks with hydrophobic ends are found to produce
inter-cluster multimers due to bridging by the hydrophilic middle blocks,
resulting in polydisperse distributions. Implications of these observations for
preparation of monodispersed nanoparticles and, potentially, understanding of
the quaternary structure of proteins are discussed.Comment: 4 pages, 4 PS figures. Accepted for publication in EP
Yang-Baxter equation on two-dimensional lattice and some infinite dimensional algebras
We show that the Yang-Baxter equation is equivalent to the associativity of the algebra generated by non-commuting link operators. Starting from these link operators we build out the (FFZ) algebras, the is derived by considering a special combination of the generators of (FFZ) algebra
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