2,325 research outputs found
Non-uniform transition conductivity of superconducting ceramic
The effects of microstructural variations on the superconducting properties of SmBa2Cu3Ox are investigated. A scanning eddy current probe revealed the onset and growth of a normal conducting region. Resistance versus temperature measurements taken at different regions of the sample support the concept of a physically mixed state system. Regional variations in porosity and grain size distributions affect the observed superconducting transition
Semiclassical limit of the entanglement in closed pure systems
We discuss the semiclassical limit of the entanglement for the class of
closed pure systems. By means of analytical and numerical calculations we
obtain two main results: (i) the short-time entanglement does not depend on
Planck's constant and (ii) the long-time entanglement increases as more
semiclassical regimes are attained. On one hand, this result is in contrast
with the idea that the entanglement should be destroyed when the macroscopic
limit is reached. On the other hand, it emphasizes the role played by
decoherence in the process of emergence of the classical world. We also found
that, for Gaussian initial states, the entanglement dynamics may be described
by an entirely classical entropy in the semiclassical limit.Comment: 8 pages, 2 figures (accepted for publication in Phys. Rev. A
Information Transfer Implies State Collapse
We attempt to clarify certain puzzles concerning state collapse and
decoherence. In open quantum systems decoherence is shown to be a necessary
consequence of the transfer of information to the outside; we prove an upper
bound for the amount of coherence which can survive such a transfer. We claim
that in large closed systems decoherence has never been observed, but we will
show that it is usually harmless to assume its occurrence. An independent
postulate of state collapse over and above Schroedinger's equation and the
probability interpretation of quantum states, is shown to be redundant.Comment: 13 page
Geometric phases and quantum phase transitions
Quantum phase transition is one of the main interests in the field of
condensed matter physics, while geometric phase is a fundamental concept and
has attracted considerable interest in the field of quantum mechanics. However,
no relevant relation was recognized before recent work. In this paper, we
present a review of the connection recently established between these two
interesting fields: investigations in the geometric phase of the many-body
systems have revealed so-called "criticality of geometric phase", in which
geometric phase associated with the many-body ground state exhibits
universality, or scaling behavior in the vicinity of the critical point. In
addition, we address the recent advances on the connection of some other
geometric quantities and quantum phase transitions. The closed relation
recently recognized between quantum phase transitions and some of geometric
quantities may open attractive avenues and fruitful dialog between different
scientific communities.Comment: Invited review article for IJMPB; material covered till June 2007; 10
page
Voneinander Lernen: Ein Handbuch für Sprachlehrerverbände
The publication is aimed at those involved in the running of language teacher associations at international, national, regional and local levels. This may include paid employees or, more frequently, volunteers. It provides guidance on the effective running and networking of associations. It encourages language teacher associations to collaborate in order to support teachers more effectively, and to contribute to improvements in the quality of language teaching. It enables language teachers across the world to share their own ideas, to be involved in research, and to learn about the cutting-edge work of the ECML and its European projects
Learning from each other: A handbook for language teacher associations
The publication is aimed at those involved in the running of language teacher associations at international, national, regional and local levels. This may include paid employees or, more frequently, volunteers. It provides guidance on the effective running and networking of associations. It encourages language teacher associations to collaborate in order to support teachers more effectively, and to contribute to improvements in the quality of language teaching. It enables language teachers across the world to share their own ideas, to be involved in research, and to learn about the cutting-edge work of the ECML and its European project
Apprendre les uns des autres: Manuel pour les associations de professeurs de langues
The publication is aimed at those involved in the running of language teacher associations at international, national, regional and local levels. This may include paid employees or, more frequently, volunteers. It provides guidance on the effective running and networking of associations. It encourages language teacher associations to collaborate in order to support teachers more effectively, and to contribute to improvements in the quality of language teaching. It enables language teachers across the world to share their own ideas, to be involved in research, and to learn about the cutting-edge work of the ECML and its European project
Loschmidt Echo and Berry phase of the quantum system coupled to the XY spin chain: Proximity to quantum phase transition
We study the Loschmidt echo (LE) of a coupled system consisting of a central
spin and its surrounding environment described by a general XY spin-chain
model. The quantum dynamics of the LE is shown to be remarkably influenced by
the quantum criticality of the spin chain. In particular, the decaying behavior
of the LE is found to be controlled by the anisotropy parameter of the spin
chain. Furthermore, we show that due to the coupling to the spin chain, the
ground-state Berry phase for the central spin becomes nonanalytical and its
derivative with respect to the magnetic parameter in spin chain
diverges along the critical line , which suggests an alternative
measurement of the quantum criticality of the spin chain.Comment: 15 pages, 5 figure
Mean-Field Dynamics: Singular Potentials and Rate of Convergence
We consider the time evolution of a system of identical bosons whose
interaction potential is rescaled by . We choose the initial wave
function to describe a condensate in which all particles are in the same
one-particle state. It is well known that in the mean-field limit the quantum -body dynamics is governed by the nonlinear Hartree
equation. Using a nonperturbative method, we extend previous results on the
mean-field limit in two directions. First, we allow a large class of singular
interaction potentials as well as strong, possibly time-dependent external
potentials. Second, we derive bounds on the rate of convergence of the quantum
-body dynamics to the Hartree dynamics.Comment: Typos correcte
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