36,547 research outputs found
Simple sentences, substitutions, and mistaken evaluations
Many competent speakers initially judge that (i) is true and (ii) is false, though
they know that (iii) is true.
(i) Superman leaps more tall buildings than Clark Kent.
(ii) Superman leaps more tall buildings than Superman.
(iii) Superman is identical with Clark Kent.
Semantic explanations of these intuitions say that (i) and (ii) really can differ in truthvalue.
Pragmatic explanations deny this, and say that the intuitions are due to misleading
implicatures. This paper argues that both explanations are incorrect. (i) and (ii) cannot
differ in truth-value, yet the intuitions are not due to implicatures, but rather to mistakes
in evaluating (i) and (ii)
Creation of Entanglement by Interaction with a Common Heat Bath
I show that entanglement between two qubits can be generated if the two
qubits interact with a common heat bath in thermal equilibrium, but do not
interact directly with each other. In most situations the entanglement is
created for a very short time after the interaction with the heat bath is
switched on, but depending on system, coupling, and heat bath, the entanglement
may persist for arbitrarily long times. This mechanism sheds new light on the
creation of entanglement. A particular example of two quantum dots in a closed
cavity is discussed, where the heat bath is given by the blackbody radiation.Comment: 4 revtex pages, 1 eps figure; replaced with published version; short
discussion on entanglement distillation adde
Decoherence in a system of many two--level atoms
I show that the decoherence in a system of degenerate two--level atoms
interacting with a bosonic heat bath is for any number of atoms governed by
a generalized Hamming distance (called ``decoherence metric'') between the
superposed quantum states, with a time--dependent metric tensor that is
specific for the heat bath.The decoherence metric allows for the complete
characterization of the decoherence of all possible superpositions of
many-particle states, and can be applied to minimize the over-all decoherence
in a quantum memory. For qubits which are far apart, the decoherence is given
by a function describing single-qubit decoherence times the standard Hamming
distance. I apply the theory to cold atoms in an optical lattice interacting
with black body radiation.Comment: replaced with published versio
Pseudo resonance induced quasi-periodic behavior in stochastic threshold dynamics
Here we present a simple stochastic threshold model consisting of a
deterministic slowly decaying term and a fast stochastic noise term. The
process shows a pseudo-resonance, in the sense that for small and large
intensities of the noise the signal is irregular and the distribution of
threshold crossings is broad, while for a tuned intermediate value of noise
intensity the signal becomes quasi-periodic and the distribution of threshold
crossings is narrow. The mechanism captured by the model might be relevant for
explaining apparent quasi-periodicity of observed climatic variations where no
internal or external periodicities can be identified.Comment: 8 pages, 4 figures, to appear in Stochastics and Dynamic
Design Space Pruning Techniques for Low-Thrust, Multiple Asteroid Rendezvous Trajectory Design
AAS/AIAA Astrodynamics Specialist Conference, August 2007, Mackinac Island, MI.In 2006, the 2nd Global Trajectory Optimization Competition (GTOC2) posed a
âGrand Asteroid Tourâ trajectory optimization problem, where participants were
required to find the best possible low-thrust trajectory that would rendezvous
with one asteroid from each of four defined groups. As a first step, most teams
employed some form of design space pruning, in order to reduce the overall
number of possible asteroid combinations. Because of the large size of the
problem, teams were not able to determine if their pruning technique had
successfully eliminated only bad solutions from the design space. Therefore, a
small subset of the GTOC2 problem was analyzed, and several design space
pruning techniques were applied to determine their effectiveness. The results
indicate that the pruning techniques chosen by the participants likely eliminated
good solutions from the design space, because they either did not accurately
represent the low-thrust problem or could not be considered independently
without the effect of other factors
Cooperative spontaneous emission from indistinguishable atoms in arbitrary motional quantum states
We investigate superradiance and subradiance of indistinguishable atoms with
quantized motional states, starting with an initial total state that factorizes
over the internal and external degrees of freedom of the atoms. Due to the
permutational symmetry of the motional state, the cooperative spontaneous
emission, governed by a recently derived master equation [F. Damanet et al.,
Phys. Rev. A 93, 022124 (2016)], depends only on two decay rates and
and a single parameter describing the
dipole-dipole shifts. We solve the dynamics exactly for atoms,
numerically for up to 30 atoms, and obtain the large--limit by amean-field
approach. We find that there is a critical difference that
depends on beyond which superradiance is lost. We show that exact
non-trivial dark states (i.e. states other than the ground state with vanishing
spontaneous emission) only exist for , and that those states
(dark when ) are subradiant when .Comment: 14 pages, 8 figure
Boundary conditions at the mobility edge
It is shown that the universal behavior of the spacing distribution of
nearest energy levels at the metal--insulator Anderson transition is indeed
dependent on the boundary conditions. The spectral rigidity also
depends on the boundary conditions but this dependence vanishes at high energy
. This implies that the multifractal exponent of the participation
ratio of wave functions in the bulk is not affected by the boundary conditions.Comment: 4 pages of revtex, new figures, new abstract, the text has been
changed: The large energy behavior of the number variance has been found to
be independent of the boundary condition
Transverse energy per charged particle at relativistic energies from a statistical model with expansion
Transverse energy and charged particle pseudorapidity densities at
midrapidity and their ratio, ,
are evaluated in a statistical model with longitudinal and transverse flows for
the wide range of colliders, from AGS to RHIC at GeV.
Evaluations are done at freeze-out parameters established independently from
fits to observed particle yields and spectra. Decays of hadron
resonances are treated thoroughly and are included in derivations of
and . The predictions of the model
agree well with the experimental data. However, some (explicable)
overestimation of the ratio has been observed.Comment: Revtex, 11 pages, 1 figure (included), The revised version with the
title changed and new conclusions added, to appear in Eur. Phys. J.
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