6,068 research outputs found
Decoherence-Based Quantum Zeno Effect in a Cavity-QED System
We present a decoherence-based interpretation for the quantum Zeno effect
(QZE) where measurements are dynamically treated as dispersive couplings of the
measured system to the apparatus, rather than the von Neumann's projections. It
is found that the explicit dependence of the survival probability on the
decoherence time quantitatively distinguishes this dynamic QZE from the usual
one based on projection measurements. By revisiting the cavity-QED experiment
of the QZE [J. Bernu, et al., Phys. Rev. Lett, 101, 180402 (2008)], we suggest
an alternative scheme to verify our theoretical consideration that frequent
measurements slow down the increase of photon number inside a microcavity due
to the nondemolition couplings with the atoms in large detuning.Comment: 4 pages, 3 figure
Different sensing mechanisms in single wire and mat carbon nanotubes chemical sensors
Chemical sensing properties of single wire and mat form sensor structures
fabricated from the same carbon nanotube (CNT) materials have been compared.
Sensing properties of CNT sensors were evaluated upon electrical response in
the presence of five vapours as acetone, acetic acid, ethanol, toluene, and
water. Diverse behaviour of single wire CNT sensors was found, while the mat
structures showed similar response for all the applied vapours. This indicates
that the sensing mechanism of random CNT networks cannot be interpreted as a
simple summation of the constituting individual CNT effects, but is associated
to another robust phenomenon, localized presumably at CNT-CNT junctions, must
be supposed.Comment: 12 pages, 5 figures,Applied Physics A: Materials Science and
Processing 201
Fibre bundle formulation of nonrelativistic quantum mechanics. III. Pictures and integrals of motion
We propose a new systematic fibre bundle formulation of nonrelativistic
quantum mechanics. The new form of the theory is equivalent to the usual one
but it is in harmony with the modern trends in theoretical physics and
potentially admits new generalizations in different directions. In it a pure
state of some quantum system is described by a state section (along paths) of a
(Hilbert) fibre bundle. It's evolution is determined through the bundle
(analogue of the) Schr\"odinger equation. Now the dynamical variables and the
density operator are described via bundle morphisms (along paths). The
mentioned quantities are connected by a number of relations derived in this
work.
In this third part of our series we investigate the bundle analogues of the
conventional pictures of motion. In particular, there are found the state
sections and bundle morphisms corresponding to state vectors and observables
respectively. The equations of motion for these quantities are derived too.
Using the results obtained, we consider from the bundle view-point problems
concerning the integrals of motion. An invariant (bundle) necessary and
sufficient conditions for a dynamical variable to be an integral of motion are
found.Comment: 19 standard (11pt, A4) LaTeX 2e pages. The packages AMS-LaTeX and
amsfonts are required. New references and comments are added. Minor style
chages. Continuation of quant-ph/9803083, quant-ph/9803084 and
quant-ph/9804062. For continuation of the series view
http://www.inrne.bas.bg/mathmod/bozhome
On the universality of distribution of ranked cluster masses at critical percolation
The distribution of masses of clusters smaller than the infinite cluster is
evaluated at the percolation threshold. The clusters are ranked according to
their masses and the distribution of the scaled masses M for any
rank r shows a universal behaviour for different lattice sizes L (D is the
fractal dimension). For different ranks however, there is a universal
distribution function only in the large rank limit, i.e., (y and are defined in the text), where the
universal scaling function g is found to be Gaussian in nature.Comment: 4 pages, to appear in J. Phys.
Promote cooperation by localised small-world communication
The emergence and maintenance of cooperation within sizable groups of
unrelated humans offer many challenges for our understanding. We propose that
the humans' capacity of communication, such as how many and how far away the
fellows can build up mutual communications, may affect the evolution of
cooperation. We study this issue by means of the public goods game (PGG) with a
two-layered network of contacts. Players obtain payoffs from five-person public
goods interactions on a square lattice (the interaction layer). Also, they
update strategies after communicating with neighbours in learning layer, where
two players build up mutual communication with a power law probability
depending on their spatial distance. Our simulation results indicate that the
evolution of cooperation is indeed sensitive to how players choose others to
communicate with, including the amount as well as the locations. The tendency
of localised communication is proved to be a new mechanism to promote
cooperation.Comment: 6 pages, 4 figure
Smooth analysis of the condition number and the least singular value
Let \a be a complex random variable with mean zero and bounded variance.
Let be the random matrix of size whose entries are iid copies of
\a and be a fixed matrix of the same size. The goal of this paper is to
give a general estimate for the condition number and least singular value of
the matrix , generalizing an earlier result of Spielman and Teng for
the case when \a is gaussian.
Our investigation reveals an interesting fact that the "core" matrix does
play a role on tail bounds for the least singular value of . This
does not occur in Spielman-Teng studies when \a is gaussian.
Consequently, our general estimate involves the norm .
In the special case when is relatively small, this estimate is nearly
optimal and extends or refines existing results.Comment: 20 pages. An erratum to the published version has been adde
Effect of 3d-doping on the electronic structure of BaFe2As2
The electronic structure of BaFe2As2 doped with Co, Ni, and Cu has been
studied by a variety of experimental and theoretical methods, but a clear
picture of the dopant 3d states has not yet emerged. Herein we provide
experimental evidence of the distribution of Co, Ni, and Cu 3d states in the
valence band. We conclude that the Co and Ni 3d states provide additional free
carriers to the Fermi level, while the Cu 3d states are found at the bottom of
the valence band in a localized 3d10 shell. These findings help shed light on
why superconductivity can occur in BaFe2As2 doped with Co and Ni but not Cu.Comment: 18 pages, 8 figure
Probability Distribution of the Shortest Path on the Percolation Cluster, its Backbone and Skeleton
We consider the mean distribution functions Phi(r|l), Phi(B)(r|l), and
Phi(S)(r|l), giving the probability that two sites on the incipient percolation
cluster, on its backbone and on its skeleton, respectively, connected by a
shortest path of length l are separated by an Euclidean distance r. Following a
scaling argument due to de Gennes for self-avoiding walks, we derive analytical
expressions for the exponents g1=df+dmin-d and g1B=g1S-3dmin-d, which determine
the scaling behavior of the distribution functions in the limit x=r/l^(nu) much
less than 1, i.e., Phi(r|l) proportional to l^(-(nu)d)x^(g1), Phi(B)(r|l)
proportional to l^(-(nu)d)x^(g1B), and Phi(S)(r|l) proportional to
l^(-(nu)d)x^(g1S), with nu=1/dmin, where df and dmin are the fractal dimensions
of the percolation cluster and the shortest path, respectively. The theoretical
predictions for g1, g1B, and g1S are in very good agreement with our numerical
results.Comment: 10 pages, 3 figure
Destruction of states in quantum mechanics
A description of destruction of states on the grounds of quantum mechanics
rather than quantum field theory is proposed. Several kinds of maps called
supertraces are defined and used to describe the destruction procedure. The
introduced algorithm can be treated as a supplement to the von Neumann-Lueders
measurement. The discussed formalism may be helpful in a description of EPR
type experiments and in quantum information theory.Comment: 14 pp, 1 eps figure, LaTeX2e using iopart class. Final version, will
be published in J. Phys. A: Math. Ge
On EPR paradox, Bell's inequalities and experiments which prove nothing
This article shows that the there is no paradox. Violation of Bell's
inequalities should not be identified with a proof of non locality in quantum
mechanics. A number of past experiments is reviewed, and it is concluded that
the experimental results should be re-evaluated. The results of the experiments
with atomic cascade are shown not to contradict the local realism. The article
points out flaws in the experiments with down-converted photons. The
experiments with neutron interferometer on measuring the "contextuality" and
Bell-like inequalities are analyzed, and it is shown that the experimental
results can be explained without such notions. Alternative experiment is
proposed to prove the validity of local realism.Comment: 27 pages, 8 figures. I edited a little the text and abstract I
corrected equations (49) and (50
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