642 research outputs found
Quantum state diffusion, measurement and second quantization
Realistic dynamical theories of measurement based on the diffusion of quantum
states are nonunitary, whereas quantum field theory and its generalizations are
unitary. This problem in the quantum field theory of quantum state diffusion
(QSD) appears already in the Lagrangian formulation of QSD as a classical
equation of motion, where Liouville's theorem does not apply to the usual field
theory formulation. This problem is resolved here by doubling the number of
freedoms used to represent a quantum field. The space of quantum fields is then
a classical configuration space, for which volume need not be conserved,
instead of the usual phase space, to which Liouville's theorem applies. The
creation operator for the quantized field satisfies the QSD equations, but the
annihilation operator does not satisfy the conjugate eqation. It appears only
in a formal role.Comment: 10 page
Superconductivity in Weyl semimetal NbP: Bulk vs. surface
Transition metal monopnictides belong to the new class of semimetals where the bulk properties are determined by the presence of pairs of nodes with different chirality formed by linear dispersive states in the k-space. Beside the anomaly in the bulk magnetotransport superconductivity is frequently found in some Weyl semimetals. We found signatures of superconductivity in ac and dc magnetization measurements of highly pure and stoichiometric NbP powder. We determined the lower and upper critical field and the Ginzburg-Landau parameter. The relative small superconducting volume fraction is related to either effect of finite grain size and/or surface superconductivity. The last mentioned may originate from either off stoichiometric (Nb-rich) surface layers or a strained surface with different electronic properties. Furthermore the intrinsic normal state susceptibility is determined taking into account a paramagnetic contribution of a few ppm of magnetic impurities
ODEbase: A Repository of ODE Systems for Systems Biology
Recently, symbolic computation and computer algebra systems have beensuccessfully applied in systems biology, especially in chemical reactionnetwork theory. One advantage of symbolic computation is its potential forqualitative answers to biological questions. Qualitative methods analyzedynamical input systems as formal objects, in contrast to investigating onlypart of the state space, as is the case with numerical simulation. However,symbolic computation tools and libraries have a different set of requirementsfor their input data than their numerical counterparts. A common format used inmathematical modeling of biological processes is SBML. We illustrate that theuse of SBML data in symbolic computation requires significant pre-processing,incorporating external biological and mathematical expertise. ODEbase provideshigh quality symbolic computation input data derived from established existingbiomodels, covering in particular the BioModels database.<br
Schr\"odinger's pure-state steering completed
Schroedinger investigated entanglement in two-particle state vectors by
assuming measurement finding out if the nearby particle is in a given state
vector or not. Without interaction with the distant particle, just on account
of the entanglement, the distant particle is steered into a certain state
vector. In Schroedinger's finite-dimensional case thus any distant-particle
state vector can be reached. This theory was extended to infinite-dimensional
spaces by the author. The present article completes the extension by throwing
light on the fine structure of steering.Comment: 10 pages, Latex2e, no figure
Strong Correlations in Electron Doped Phthalocyanine Conductors Near Half Filling
We propose that electron doped nontransition metal-phthalocyanines (MPc) like
ZnPc and MgPc, similar to those very recently reported, should constitute novel
strongly correlated metals. Due to orbital degeneracy, Jahn-Teller coupling and
Hund's rule exchange, and with a large on-site Coulomb repulsion, these
molecular conductors should display, particularly near half filling at two
electrons/molecule, very unconventional properties, including Mott insulators,
strongly correlated superconductivity, and other intriguing phases.Comment: 4 pages, 1 figure, submited to PR
Algorithmic Reduction of Biological Networks With Multiple Time Scales
We present a symbolic algorithmic approach that allows to compute invariant manifolds and corresponding reduced systems for differential equations modeling biological networks which comprise chemical reaction networks for cellular biochemistry, and compartmental models for pharmacology, epidemiology and ecology. Multiple time scales of a given network are obtained by scaling, based on tropical geometry. Our reduction is mathematically justified within a singular perturbation setting using a recent result by Cardin and Teixeira. The existence of invariant manifolds is subject to hyperbolicity conditions, which we test algorithmically using Hurwitz criteria. We finally obtain a sequence of nested invariant manifolds and respective reduced systems on those manifolds. Our theoretical results are generally accompanied by rigorous algorithmic descriptions suitable for direct implementation based on existing off-the-shelf software systems, specifically symbolic computation libraries and Satisfiability Modulo Theories solvers. We present computational examples taken from the well-known BioModels database using our own prototypical implementations
Passage-time distributions from a spin-boson detector model
The passage-time distribution for a spread-out quantum particle to traverse a
specific region is calculated using a detailed quantum model for the detector
involved. That model, developed and investigated in earlier works, is based on
the detected particle's enhancement of the coupling between a collection of
spins (in a metastable state) and their environment. We treat the continuum
limit of the model, under the assumption of the Markov property, and calculate
the particle state immediately after the first detection. An explicit example
with 15 boson modes shows excellent agreement between the discrete model and
the continuum limit. Analytical expressions for the passage-time distribution
as well as numerical examples are presented. The precision of the measurement
scheme is estimated and its optimization discussed. For slow particles, the
precision goes like , which improves previous estimates,
obtained with a quantum clock model.Comment: 11 pages, 6 figures; minor changes, references corrected; accepted
for publication in Phys. Rev.
(LaCrO3)m/SrCrO3 superlattices as transparent p-type semiconductors with finite magnetization
The electronic and magnetic properties of (LaCrO3)m/SrCrO3 superlattices are investigated using first principles calculations. We show that the magnetic moments in the two CrO2 layers sandwiching the SrO layer compensate each other for even m but give rise to a finite magnetization for odd m, which is explained by charge ordering with Cr3+ and Cr4+ ions arranged in a checkerboard pattern. The Cr4+ ions induce in-gap hole states at the interface, implying that the transparent superlattices are p-type semiconductors. The availability of transparent p-type semiconductors with finite magnetization enables the fabrication of transparent magnetic diodes and transistors, for example, with a multitude of potential technological applications
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