32,522 research outputs found
Exact Bethe Ansatz solution for chains with non- invariant open boundary conditions
The Nested Bethe Ansatz is generalized to open and independent boundary
conditions depending on two continuous and two discrete free parameters. This
is used to find the exact eigenvectors and eigenvalues of the vertex
models and spin chains with such boundary conditions. The solution is
found for all diagonal families of solutions to the reflection equations in all
possible combinations. The Bethe ansatz equations are used to find de first
order finite size correction.Comment: Two references adde
Combinatorics of lattice paths with and without spikes
We derive a series of results on random walks on a d-dimensional hypercubic
lattice (lattice paths). We introduce the notions of terse and simple paths
corresponding to the path having no backtracking parts (spikes). These paths
label equivalence classes which allow a rearrangement of the sum over paths.
The basic combinatorial quantities of this construction are given. These
formulas are useful when performing strong coupling (hopping parameter)
expansions of lattice models. Some applications are described.Comment: Latex. 25 page
Excitations from Filled Landau Levels in Graphene
We consider graphene in a strong perpendicular magnetic field at zero
temperature with an integral number of filled Landau levels and study the
dispersion of single particle-hole excitations. We first analyze the two-body
problem of a single Dirac electron and hole in a magnetic field interacting via
Coulomb forces. We then turn to the many-body problem, where particle-hole
symmetry and the existence of two valleys lead to a number of effects peculiar
to graphene. We find that the coupling together of a large number of low-lying
excitations leads to strong many-body corrections, which could be observed in
inelastic light scattering or optical absorption. We also discuss in detail how
the appearance of different branches in the exciton dispersion is sensitive to
the number of filled spin and valley sublevels.Comment: 15 pages, 19 figure
Soliton tunneling with sub-barrier kinetic energies
We investigate (theoretically and numerically) the dynamics of a soliton
moving in an asymmetrical potential well with a finite barrier. For large
values of the width of the well, the width of the barrier and/or the height of
the barrier, the soliton behaves classically. On the other hand, we obtain the
conditions for the existence of soliton tunneling with sub-barrier kinetic
energies. We apply these results to the study of soliton propagation in
disordered systems.Comment: 6 eps figures. To appear in Physical Review E (Rapid Communications
Confinement of electrons in layered metals
We analyze the out of plane hopping in models of layered systems where the
in--plane properties deviate from Landau's theory of a Fermi liquid. We show
that the hopping term acquires a non trivial energy dependence, due to the
coupling to in plane excitations, and can be either relevant or irrelevant at
low energies or temperatures. The latter is always the case if the Fermi level
lies close to a saddle point in the dispersion relation.Comment: 4 pages, 1 eps figur
Description with a Screened Potential
Recent lattice QCD calculations suggest a rather abrupt transition in the
confinig potential from a linear to a constant behavior. We analyze the effects
of such a fast deconfinement in the simplest non-relativistic system,
bottomonium.Comment: 4 pages. Presented at MENU04, Beijing 2004. To be published by IJMP
Heralded multiphoton states with coherent spin interactions in waveguide QED
WaveguideQEDoffers the possibility of generating strong coherent atomic
interactions either through appropriate atomic configurations in the
dissipative regime or in the bandgap regime. In this work, we show how to
harness these interactions in order to herald the generation of highly
entangled atomic states, which afterwards can be mapped to generate single mode
multi-photonic states with high fidelities.Weintroduce two protocols for the
preparation of the atomic states, we discuss their performance and compare them
to previous proposals. In particular, we show that one of them reaches high
probability of success for systems with many atoms but low Purcell factors
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