1,155 research outputs found
Generalized Quantum Theory: Overview and Latest Developments
The main formal structures of Generalized Quantum Theory are summarized.
Recent progress has sharpened some of the concepts, in particular the notion of
an observable, the action of an observable on states (putting more emphasis on
the role of proposition observables), and the concept of generalized
entanglement. Furthermore, the active role of the observer in the structure of
observables and the partitioning of systems is emphasized.Comment: 14 pages, update in reference
Enhanced Charge and Spin Currents in the One-Dimensional Disordered Mesoscopic Hubbard Ring
We consider a one-dimensional mesoscopic Hubbard ring with and without
disorder and compute charge and spin stiffness as a measure of the permanent
currents. For finite disorder we identify critical disorder strength beyond
which the charge currents in a system with repulsive interactions are {\em
larger} than those for a free system. The spin currents in the disordered
repulsive Hubbard model are enhanced only for small , where the magnetic
state of the system corresponds to a charge density wave pinned to the
impurities. For large , the state of the system corresponds to localized
isolated spins and the spin currents are found to be suppressed. For the
attractive Hubbard model we find that the charge currents are always suppressed
compared to the free system at all length scales.Comment: 20 RevTeX 3.0 pages, 8 figures NOT include
Transport Properties of a One-Dimensional Two-Component Quantum Liquid with Hyperbolic Interactions
We present an investigation of the sinh-cosh (SC) interaction model with
twisted boundary conditions. We argue that, when unlike particles repel, the SC
model may be usefully viewed as a Heisenberg-Ising fluid with moving
Heisenberg-Ising spins. We derive the Luttinger liquid relation for the
stiffness and the susceptibility, both from conformal arguments, and directly
from the integral equations. Finally, we investigate the opening and closing of
the ground state gaps for both SC and Heisenberg-Ising models, as the
interaction strength is varied.Comment: 10 REVTeX pages + 4 uuencoded figures, UoU-002029
On the concept of pressure in quantum mechanics
Heat and work are fundamental concepts for thermodynamical systems. When
these are scaled down to the quantum level they require appropriate embeddings.
Here we show that the dependence of the particle spectrum on system size giving
rise to a formal definition of pressure can, indeed, be correlated with an
external mechanical degree of freedom, modelled as a spatial coordinate of a
quantum oscillator. Under specific conditions this correlation is reminiscent
of that occurring in the classical manometer.Comment: 7 pages, 3 figure
The Poisson Bracket for Poisson Forms in Multisymplectic Field Theory
We present a general definition of the Poisson bracket between differential
forms on the extended multiphase space appearing in the geometric formulation
of first order classical field theories and, more generally, on exact
multisymplectic manifolds. It is well defined for a certain class of
differential forms that we propose to call Poisson forms and turns the space of
Poisson forms into a Lie superalgebra.Comment: 40 pages LaTe
Electron spin relaxation in bulk GaAs for doping densities close to the metal-to-insulator transition
We have measured the electron spin relaxation rate and the integrated spin
noise power in n-doped GaAs for temperatures between 4 K and 80 K and for
doping concentrations ranging from 2.7 x 10^{-15} cm^{-3} to 8.8 x 10^{-16}
cm^{-3} using spin noise spectroscopy. The temperature dependent measurements
show a clear transition from localized to free electrons for the lower doped
samples and confirm mainly free electrons at all temperatures for the highest
doped sample. While the sample at the metal-insulator-transition shows the
longest spin relaxation time at low temperatures, a clear crossing of the spin
relaxation rates is observed at 70 K and the highest doped sample reveals the
longest spin relaxation time above 70 K.Comment: 6 pages, 4 figure
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