36 research outputs found
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
Sub-Planck spots of Schroedinger cats and quantum decoherence
Heisenberg's principle states that the product of uncertainties of
position and momentum should be no less than Planck's constant . This is
usually taken to imply that phase space structures associated with sub-Planck
() scales do not exist, or, at the very least, that they do not
matter. I show that this deeply ingrained prejudice is false: Non-local
"Schr\"odinger cat" states of quantum systems confined to phase space volume
characterized by `the classical action' develop spotty structure
on scales corresponding to sub-Planck . Such
structures arise especially quickly in quantum versions of classically chaotic
systems (such as gases, modelled by chaotic scattering of molecules), that are
driven into nonlocal Schr\"odinger cat -- like superpositions by the quantum
manifestations of the exponential sensitivity to perturbations. Most
importantly, these sub-Planck scales are physically significant: determines
sensitivity of a quantum system (or of a quantum environment) to perturbations.
Therefore sub-Planck controls the effectiveness of decoherence and
einselection caused by the environment. It may also be relevant in
setting limits on sensitivity of Schr\"odinger cats used as detectors.Comment: Published in Nature 412, 712-717 (2001