2,305 research outputs found
Critical Property of Geometric Phase in the Dicke Model
We obtain the ground-state energy level and associated geometric phase in the
Dicke model analytically by means of the Holstein-Primakoff transformation and
the boson expansion approach in the thermodynamic limit. The non-adiabatic
geometric phase induced by the photon field is derived with the time-dependent
unitary transformation. It is shown that the quantum phase transition
characterized by the non-analyticity of the geometric phase is remarkably of
the first-order. We also investigate the scaling behavior of the geometric
phase at the critical point, which can be measured in a practical experiment to
detect the quantum phase transition.Comment: 1 figur
Classical Physics and Quantum Loops
The standard picture of the loop expansion associates a factor of h-bar with
each loop, suggesting that the tree diagrams are to be associated with
classical physics, while loop effects are quantum mechanical in nature. We
discuss examples wherein classical effects arise from loop contributions and
display the relationship between the classical terms and the long range effects
of massless particles.Comment: 15 pages, 3 figure
Exotic Meson Decay Widths using Lattice QCD
A decay width calculation for a hybrid exotic meson h, with JPC=1-+, is
presented for the channel h->pi+a1. This quenched lattice QCD simulation
employs Luescher's finite box method. Operators coupling to the h and pi+a1
states are used at various levels of smearing and fuzzing, and at four quark
masses. Eigenvalues of the corresponding correlation matrices yield energy
spectra that determine scattering phase shifts for a discrete set of relative
pi+a1 momenta. Although the phase shift data is sparse, fits to a Breit-Wigner
model are attempted, resulting in a decay width of about 60 MeV when averaged
over two lattice sizes.Comment: 9 pages, 8 figures, RevTex4, minor change to Fig.
MOD/R : A knowledge assisted approach towards top-down only CMOS VLSI design
MOD/R models all views on the design space in relations. This is achieved by eliminating the package constraints, as are apparent in PCB oriented hardware description languages. Assisted by knowledge engineering it allows for a top-down, mostly hierarchical decomposition, virtually eliminating the need for bottom-up assembly
Entanglement between atomic condensates in an optical lattice: effects of interaction range
We study the area-dependent entropy and two-site entanglement for two state
Bose-Einstein condensates in a 2D optical lattice. We consider the case where
the array of two component condensates behave like an ensemble of spin-half
particles with the interaction to its nearest neighbors and next nearest
neighbors. We show how the Hamiltonian of their Bose-Einstein condensate
lattice with nearest-neighbor and next-nearest-neighbor interactions can be
mapped into a harmonic lattice. We use this to determine the entropy and
entanglement content of the lattice.Comment: 5 pages, 3 figures, title change
Spin-gap phase in nearly-half-filled one-dimensional conductors coupled with phonons
Asymptotic properties of nearly-half-filled one-dimensional conductors
coupled with phonons are studied through a renormalization group method. Due to
spin-charge coupling via electron-phonon interaction, the spin correlation
varies with filling as well as the charge correlation. Depending on the
relation between cut-off energy scales of the Umklapp process and of the
electron-phonon interaction, various phases appear. We found a metallic phase
with a spin gap and a dominant charge- density-wave correlation near half
filling between a gapless density-wave phase (like in the doped repulsive
Hubbard model) and a superconductor phase with a spin gap. The spin gap is
produced by phonon-assisted backward scatterings which are interfered with the
Umklapp process constructively or destructively depending on the character of
electron-phonon coupling.Comment: 14 pages, revtex, replaced 5 ps figures, published in PR
An alternative approach for the dynamics of polarons in one dimension
We developed a new method based on functional integration to treat the
dynamics of polarons in one-dimensional systems. We treat the acoustical and
the optical case in an unified manner, showing their differences and
similarities. The mobility and diffusion coefficients are calculated in the
Markovian approximation in the strong coupling limit.Comment: 57 page
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