827 research outputs found
Decoherence induced by a chaotic environment: A quantum walker with a complex coin
We study the differences between the process of decoherence induced by
chaotic and regular environments. For this we analyze a family of simple models
wich contain both regular and chaotic environments. In all cases the system of
interest is a "quantum walker", i.e. a quantum particle that can move on a
lattice with a finite number of sites. The walker interacts with an environment
wich has a D dimensional Hilbert space. The results we obtain suggest that
regular and chaotic environments are not distinguishable from each other in a
(short) timescale t*, wich scales with the dimensionality of the environment as
t*~log(D). Howeber, chaotic environments continue to be effective over
exponentially longer timescales while regular environments tend to reach
saturation much sooner. We present both numerical and analytical results
supporting this conclusion. The family of chaotic evolutions we consider
includes the so-called quantum multi-baker-map as a particular case.Comment: 7 pages, 8 figure
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ISO Detection of CO<sup>+</sup> toward the protostar IRAS 16293-2422
In this letter we report the detection of eight high-N rotational transitions of CO+ towards a low mass protostar, IRAS 16293-2422. The source was observed with the Long Wavelength Spectrometer on board the Infrared Space Observatory. This is the first time that CO+ has been detected in a low luminosity source and the first time that high-N lines have been detected in any source. The detection of these lines was not predicted by models and consequently, their interpretation is a challenge. We discuss the possibility that the observed CO+ emission originates in the dense inner regions illuminated by the UV field created in the accretion shock (formed by infalling material), and conclude that this is an improbable explanation. We have also considered the possibility that a strong, dissociative J-shock at ~ 500 AU from the star is the origin of the CO+ emission. This model predicts CO+ column densities in rough agreement with the observations if the magnetic field is ~ 1 mG and the shock velocity is 100 km s-1
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Detection of CO<sup>+</sup> with ISO towards the protostar IRAS16293-242
We observed the low luminosity (and low mass) protostar IRAS16293-2422 with the Long Wavelength Spectrometer on board the Infrared Space Observatory. The observed line spectrum is very reach and shows transitions of several molecules and atoms. Here we report the detection of eight high-N rotational transitions of CO+. This is the first time that CO+ has been detected in a low luminosity source and the first time that high-N lines have been detected in any source. The detection of these lines was not predicted by models and consequently, their interpretation is a challenge. We discuss the possibility that the observed CO+ emission originates in the dense inner regions illuminated by the UV field created in the accretion shock (formed by infalling material), and conclude that this is an improbable explanation. We have also considered the possibility that a strong, dissociative J-shock at ~500 AU from the star is the origin of the CO+ emission. This model predicts CO+ column densities in rough agreement with the observations if the magnetic field is ~1 mG and the shock velocity is 100 km s-1
Multifractal eigenstates of quantum chaos and the Thue-Morse sequence
We analyze certain eigenstates of the quantum baker's map and demonstrate,
using the Walsh-Hadamard transform, the emergence of the ubiquitous Thue-Morse
sequence, a simple sequence that is at the border between quasi-periodicity and
chaos, and hence is a good paradigm for quantum chaotic states. We show a
family of states that are also simply related to Thue-Morse sequence, and are
strongly scarred by short periodic orbits and their homoclinic excursions. We
give approximate expressions for these states and provide evidence that these
and other generic states are multifractal.Comment: Substantially modified from the original, worth a second download. To
appear in Phys. Rev. E as a Rapid Communicatio
Accuracy of Trace Formulas
Using quantum maps we study the accuracy of semiclassical trace formulas. The
role of chaos in improving the semiclassical accuracy, in some systems, is
demonstrated quantitatively. However, our study of the standard map cautions
that this may not be most general. While studying a sawtooth map we demonstrate
the rather remarkable fact that at the level of the time one trace even in the
presence of fixed points on singularities the trace formula may be exact, and
in any case has no logarithmic divergences observed for the quantum bakers map.
As a byproduct we introduce fantastic periodic curves akin to curlicues.Comment: 20 pages, uuencoded and gzipped, 1 LaTex text file and 9 PS files for
figure
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ISO-LWS grating spectroscopy: the case of R CrA star forming region
We present the far infrared spectra of the R CrA star forming region obtained with ISO-LWS. We collected a pointed observation on the Herbig Ae star R CrA and a raster scan covering the surrounding region, where HH100 (with its exciting source) and the pre-Main Sequence star T CrA are located. The OI 63μm and the CII 158μm lines have been detected in all the pointed positions, with a ratio consistent with PDR excitation. CO rotational lines (between Jup=14 and Jup=19) are detected on R CrA; from their intensities we derived, using a LVG model, the density and temperature of the emitting region. Other molecular transitions (OH and H2O) have been detected on the investigated objects; the derived cooling of all the molecular species is in agreement with C-shock as the likely excitation mechanism. The continuum emission of R CrA peaks around 100μm (as expected for a Herbig star) while the other sources (T CrA, HH100) show increasing continua up to ~200μm, indicating that they are probably less evolved sources
The Poincare-Birkhoff theorem in Quantum Mechanics
Quantum manifestations of the dynamics around resonant tori in perturbed
Hamiltonian systems, dictated by the Poincar\'e--Birkhoff theorem, are shown to
exist. They are embedded in the interactions involving states which differ in a
number of quanta equal to the order of the classical resonance. Moreover, the
associated classical phase space structures are mimicked in the
quasiprobability density functions and their zeros.Comment: 5 pages, 3 figures, Full resolution figures available at
http://www.df.uba.ar/users/wisniaki/publications.htm
Coarse Grained Liouville Dynamics of piecewise linear discontinuous maps
We compute the spectrum of the classical and quantum mechanical
coarse-grained propagators for a piecewise linear discontinuous map. We analyze
the quantum - classical correspondence and the evolution of the spectrum with
increasing resolution. Our results are compared to the ones obtained for a
mixed system.Comment: 11 pages, 8 figure
Probing the quantum phase transition in the Dicke model through mechanical vibrations
This paper is concerned with quantum dynamics of a system coupled to a
critical reservoir. In this context, we employ the Dicke model which is known
to exhibit a super radiant quantum phase transition (QPT) and we allow one of
the mirrors to move under a linear restoring force. The electromagnetic field
couples to the movable mirror though radiation pressure just like in typical
optomechanical setups. We show that, in the thermodynamical limit, the
super-radiant phase induces a classical driving force on the mirror without
causing decoherence.Comment: 6 pages, 3 figures, final versio
Semiclassical structure of chaotic resonance eigenfunctions
We study the resonance (or Gamow) eigenstates of open chaotic systems in the
semiclassical limit, distinguishing between left and right eigenstates of the
non-unitary quantum propagator, and also between short-lived and long-lived
states. The long-lived left (right) eigenstates are shown to concentrate as
on the forward (backward) trapped set of the classical dynamics.
The limit of a sequence of eigenstates is found
to exhibit a remarkably rich structure in phase space that depends on the
corresponding limiting decay rate. These results are illustrated for the open
baker map, for which the probability density in position space is observed to
have self-similarity properties.Comment: 4 pages, 4 figures; some minor corrections, some changes in
presentatio
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