407 research outputs found
A quantum-mechanical Maxwell's demon
A Maxwell's demon is a device that gets information and trades it in for
thermodynamic advantage, in apparent (but not actual) contradiction to the
second law of thermodynamics. Quantum-mechanical versions of Maxwell's demon
exhibit features that classical versions do not: in particular, a device that
gets information about a quantum system disturbs it in the process. In
addition, the information produced by quantum measurement acts as an additional
source of thermodynamic inefficiency. This paper investigates the properties of
quantum-mechanical Maxwell's demons, and proposes experimentally realizable
models of such devices.Comment: 13 pages, Te
Physical Complexity of Symbolic Sequences
A practical measure for the complexity of sequences of symbols (``strings'')
is introduced that is rooted in automata theory but avoids the problems of
Kolmogorov-Chaitin complexity. This physical complexity can be estimated for
ensembles of sequences, for which it reverts to the difference between the
maximal entropy of the ensemble and the actual entropy given the specific
environment within which the sequence is to be interpreted. Thus, the physical
complexity measures the amount of information about the environment that is
coded in the sequence, and is conditional on such an environment. In practice,
an estimate of the complexity of a string can be obtained by counting the
number of loci per string that are fixed in the ensemble, while the volatile
positions represent, again with respect to the environment, randomness. We
apply this measure to tRNA sequence data.Comment: 12 pages LaTeX2e, 3 postscript figures, uses elsart.cls.
Substantially improved and clarified version, includes application to EMBL
tRNA sequence dat
Quantum Theory of the Classical: Einselection, Envariance, Quantum Darwinism and Extantons
Core quantum postulates including the superposition principle and the
unitarity of evolutions are natural and strikingly simple. I show that -- when
supplemented with a limited version of predictability (captured in the textbook
accounts by the repeatability postulate) -- these core postulates can account
for all the symptoms of classicality. In particular, both objective classical
reality and elusive information about reality arise, via quantum Darwinism,
from the quantum substrate.Comment: To appear in the ENTROPY volume "Quantum Darinism and Friends" edited
by Sebastian Deffner et al.
https://www.mdpi.com/journal/entropy/special_issues/quantum_darwinism. arXiv
admin note: text overlap with arXiv:0707.283
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'Waiting for Carnot': Information and complexity
The relationship between information and complexity is analysed, by way of a detailed literature analysis. Complexity is a multi-faceted concept, with no single agreed definition. There are numerous approaches to defining and measuring complexity and organisation, all involving the idea of information. Conceptions of complexity, order, organization and âinteresting orderâ are inextricably intertwined with those of information. Shannonâs formalism captures informationâs unpredictable creative contributions to organized complexity; a full understanding of informationâs relation to structure and order is still lacking. Conceptual investigations of this topic should enrich the theoretical basis of the information science discipline, and create fruitful links with other disciplines which study the concepts of information and complexity
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
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