3,236 research outputs found
Decoherence: Concepts and Examples
We give a pedagogical introduction to the process of decoherence - the
irreversible emergence of classical properties through interaction with the
environment. After discussing the general concepts, we present the following
examples: Localisation of objects, quantum Zeno effect, classicality of fields
and charges in QED, and decoherence in gravity theory. We finally emphasise the
important interpretational features of decoherence.Comment: 24 pages, LATEX, 9 figures, needs macro lamuphys.sty, to appear in
the Proceedings of the 10th Born Symposiu
Toy models for gravitational and scalar QED decoherence
We investigate the dynamics of two quantum mechanical oscillator system-bath
toy models obtained by dimensionally truncating linearized gravity coupled to a
massive scalar field and scalar QED. The scalar-gravity toy model maps onto the
phase damped oscillator, while the scalar QED toy model approximately maps onto
an oscillator system subject to two-photon damping. The toy models provide
potentially useful insights into solving for open system quantum dynamics
relevant to the full scalar QED and weak gravitational field systems, in
particular the decoherence of initial scalar field system superposition states
Symmetries, superselection rules, and decoherence
We discuss the applicability of the programme of decoherence -- emergence of
approximate classical behaviour through interaction with the environment -- to
cases where it was suggested that the presence of symmetries would lead to
exact superselection rules. For this discussion it is useful to make a
distinction between pure symmetries and redundancies, which results from an
investigation into the constraint equations of the corresponding theories. We
discuss, in particular, superpositions of states with different charges, as
well as with different masses, and suggest how the corresponding interference
terms, although they exist in principle, become inaccessible through
decoherence.Comment: 12 pages, LATEX, Report Freiburg THEP-94/3
Problems with the Newton-Schr\"odinger Equations
We examine the origin of the Newton-Schr\"odinger equations (NSEs) that play
an important role in alternative quantum theories (AQT), macroscopic quantum
mechanics and gravity-induced decoherence. We show that NSEs for individual
particles do not follow from general relativity (GR) plus quantum field theory
(QFT). Contrary to what is commonly assumed, the NSEs are not the weak-field
(WF), non-relativistic (NR) limit of the semi-classical Einstein equation (SCE)
(this nomenclature is preferred over the `M\/oller-Rosenfeld equation') based
on GR+QFT. The wave-function in the NSEs makes sense only as that for a mean
field describing a system of particles as , not that
of a single or finite many particles. From GR+QFT the gravitational
self-interaction leads to mass renormalization, not to a non-linear term in the
evolution equations of some AQTs. The WF-NR limit of the gravitational
interaction in GR+QFT involves no dynamics. To see the contrast, we give a
derivation of the equation (i) governing the many-body wave function from
GR+QFT and (ii) for the non-relativistic limit of quantum electrodynamics
(QED). They have the same structure, being linear, and very different from
NSEs. Adding to this our earlier consideration that for gravitational
decoherence the master equations based on GR+QFT lead to decoherence in the
energy basis and not in the position basis, despite some AQTs desiring it for
the `collapse of the wave function', we conclude that the origins and
consequences of NSEs are very different, and should be clearly demarcated from
those of the SCE equation, the only legitimate representative of semiclassical
gravity, based on GR+QFT.Comment: 18 pages. Invited paper for the Focus Issue on 'Gravitational quantum
physics' in New Journal of Physic
Decoherence of Schrodinger cat states in a Luttinger liquid
Schrodinger cat states built from quantum superpositions of left or right
Luttinger fermions located at different positions in a spinless Luttinger
liquid are considered. Their decoherence rates are computed within the
bosonization approach using as environments the quantum electromagnetic field
or two or three dimensionnal acoustic phonon baths. Emphasis is put on the
differences between the electromagnetic and acoustic environments.Comment: 22 pages revtex4, 7 figures in a separate PS fil
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