1,549 research outputs found
The Chandra Fornax Survey - I: The Cluster Environment
We present the first results of a deep Chandra survey of the inner 1 degree
of the Fornax cluster of galaxies. Ten 50 ksec pointings were obtained in a
mosaic centered on the giant elliptical galaxy NGC 1399 at the nominal cluster
center. Emission and temperature maps of Fornax are presented, and an initial
study of 771 detected X-ray point sources is made. Regions as small as 100pc
are resolved. The intra-cluster gas in Fornax exhibits a highly asymmetric
morphology and temperature structure, dominated by a 180 kpc extended ``plume''
of low surface brightness, cool, ~1 keV) gas to the North-East of NGC 1399 with
a sharper edge to the South West. The elliptical galaxy NGC 1404 also exhibits
a cool halo of X-ray gas within the cluster, with a highly sharpened leading
edge as it presumably falls into the cluster, and a cometary-like tail. We
estimate that some ~200-400 point sources are physically associated with
Fornax. Confirming earlier works, we find that the globular cluster population
in NGC 1399 is highly X-ray active, extending to globulars which may in fact be
intra-cluster systems. We have also found a remarkable correlation between the
location of giant and dwarf cluster galaxies and the presence of X-ray
counterparts, such that systems inhabiting regions of low gas density are more
likely to show X-ray activity. Not only does this correlate with the asymmetry
of the intra-cluster gas but also with the axis joining the center of Fornax to
an infalling group 1 Mpc to the South-West. We suggest that Fornax may be
experiencing an intergalactic ``headwind'' due to motion relative to the
surrounding large-scale structure.Comment: 35 pages, 15 figures, submitted to ApJ. Most figures not included
owing to severe compression degradation - we strongly recommend downloading
the full resolution paper from
http://www.astro.columbia.edu/~caleb/ms_highres.pdf (1.9Mb
Decoherence and the Loschmidt echo
Environment--induced decoherence causes entropy increase. It can be
quantified using, e.g., the purity . When the
Hamiltonian of a quantum system is perturbed, its sensitivity to such
perturbation can be measured by the Loschmidt echo . It is given by
the average squared overlap between the perturbed and unperturbed state. We
describe the relation between the temporal behavior of and . In this way we show that the decay of the Loschmidt echo can be analyzed
using tools developed in the study of decoherence. In particular, for systems
with a classically chaotic Hamiltonian the decay of and
has a regime where it is dominated by the classical Lyapunov exponent
Consistent quantum mechanics admits no mereotopology
It is standardly assumed in discussions of quantum theory that physical
systems can be regarded as having well-defined Hilbert spaces. It is shown here
that a Hilbert space can be consistently partitioned only if its components are
assumed not to interact. The assumption that physical systems have well-defined
Hilbert spaces is, therefore, physically unwarranted.Comment: 10 pages; to appear in Axiomathe
What is "system": the information-theoretic arguments
The problem of "what is 'system'?" is in the very foundations of modern
quantum mechanics. Here, we point out the interest in this topic in the
information-theoretic context. E.g., we point out the possibility to manipulate
a pair of mutually non-interacting, non-entangled systems to employ
entanglement of the newly defined '(sub)systems' consisting the one and the
same composite system. Given the different divisions of a composite system into
"subsystems", the Hamiltonian of the system may perform in general
non-equivalent quantum computations. Redefinition of "subsystems" of a
composite system may be regarded as a method for avoiding decoherence in the
quantum hardware. In principle, all the notions refer to a composite system as
simple as the hydrogen atom.Comment: 13 pages, no figure
On the Definition of Decoherence
We examine the relationship between the decoherence of quantum-mechanical
histories of a closed system (as discussed by Gell-Mann and Hartle) and
environmentally-induced diagonalization of the density operator for an open
system. We study a definition of decoherence which incorporates both of these
ideas, and show that it leads to a consistent probabilistic interpretation of
the reduced density operator.Comment: 10 pages, LaTeX, SJSU/TP-93-1
Environment--Induced Decoherence, Classicality and Consistency of Quantum Histories
We prove that for an open system, in the Markovian regime, it is always
possible to construct an infinite number of non trivial sets of histories that
exactly satisfy the probability sum rules. In spite of being perfectly
consistent, these sets manifest a very non--classical behavior: they are quite
unstable under the addition of an extra instant to the list of times defining
the history. To eliminate this feature --whose implications for the
interpretation of the formalism we discuss-- and to achieve the stability that
characterizes the quasiclassical domain, it is necessary to separate the
instants which define the history by time intervals significantly larger than
the typical decoherence time. In this case environment induced superselection
is very effective and the quasiclassical domain is characterized by histories
constructed with ``pointer projectors''.Comment: 32 pages (1 figure, postcript included at the end: use epsf.tex and
follow instructions before Texing) LA-UR-93-141
Matter-Wave Decoherence due to a Gas Environment in an Atom Interferometer
Decoherence due to scattering from background gas particles is observed for
the first time in a Mach-Zehnder atom interferometer, and compared with
decoherence due to scattering photons. A single theory is shown to describe
decoherence due to scattering either atoms or photons. Predictions from this
theory are tested by experiments with different species of background gas, and
also by experiments with different collimation restrictions on an atom beam
interferometer.Comment: 4 pages, 3 figures, accepted to PR
Decoherence, Chaos, and the Correspondence Principle
We present evidence that decoherence can produce a smooth
quantum-to-classical transition in nonlinear dynamical systems. High-resolution
tracking of quantum and classical evolutions reveals differences in expectation
values of corresponding observables. Solutions of master equations demonstrate
that decoherence destroys quantum interference in Wigner distributions and
washes out fine structure in classical distributions bringing the two closer
together. Correspondence between quantum and classical expectation values is
also re-established.Comment: 4 pages, 2 figures (color figures embedded at low resolution), uses
RevTeX plus macro (included). Phys. Rev. Lett. (in press
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