2,598 research outputs found
Philosophical Aspects of Quantum Information Theory
Quantum information theory represents a rich subject of discussion for those
interested in the philosphical and foundational issues surrounding quantum
mechanics for a simple reason: one can cast its central concerns in terms of a
long-familiar question: How does the quantum world differ from the classical
one? Moreover, deployment of the concepts of information and computation in
novel contexts hints at new (or better) means of understanding quantum
mechanics, and perhaps even invites re-assessment of traditional material
conceptions of the basic nature of the physical world. In this paper I review
some of these philosophical aspects of quantum information theory, begining
with an elementary survey of the theory, seeking to highlight some of the
principles and heuristics involved. We move on to a discussion of the nature
and definition of quantum information and deploy the findings in discussing the
puzzles surrounding teleportation. The final two sections discuss,
respectively, what one might learn from the development of quantum computation
(both about the nature of quantum systems and about the nature of computation)
and consider the impact of quantum information theory on the traditional
foundational questions of quantum mechanics (treating of the views of
Zeilinger, Bub and Fuchs, amongst others).Comment: LaTeX; 55pp; 3 figs. Forthcoming in Rickles (ed.) The Ashgate
Companion to the New Philosophy of Physic
Non-locality and gauge freedom in Deutsch and Hayden's formulation of quantum mechanics
Deutsch and Hayden have proposed an alternative formulation of quantum
mechanics which is completely local. We argue that their proposal must be
understood as having a form of `gauge freedom' according to which
mathematically distinct states are physically equivalent. Once this gauge
freedom is taken into account, their formulation is no longer local.Comment: 3 page
Nonlocality and information flow: The approach of Deutsch and Hayden
Deutsch and Hayden claim to have provided an account of quantum mechanics
which is particularly local, and which clarifies the nature of information
transmission in entangled quantum systems. In this paper, a perspicuous
description of their formalism is offered and their claim assessed. It proves
essential to distinguish, as Deutsch and Hayden do not, between two ways of
interpreting the formalism. On the first, conservative, interpretation, no
benefits with respect to locality accrue that are not already available on
either an Everettian or a statistical interpretation; and the conclusions
regarding information flow are equivocal. The second, ontological,
interpretation, offers a framework with the novel feature that global
properties of quantum systems are reduced to local ones; but no conclusions
follow concerning information flow in more standard quantum mechanics.Comment: 26 pages, LaTeX, uses amsmath; 4 .eps figure
Quantum Mechanics on Spacetime I: Spacetime State Realism
What ontology does realism about the quantum state suggest? The main extant
view in contemporary philosophy of physics is wave-function realism. We
elaborate the sense in which wave-function realism does provide an ontological
picture; and defend it from certain objections that have been raised against
it. However, there are good reasons to be dissatisfied with wave-function
realism, as we go on to elaborate. This motivates the development of an
opposing picture: what we call spacetime state realism; a view which takes the
states associated to spacetime regions as fundamental. This approach enjoys a
number of beneficial features, although, unlike wave-function realism, it
involves non-separability at the level of fundamental ontology. We investigate
the pros and cons of this non-separability, arguing that it is a quite
acceptable feature; even one which proves fruitful in the context of
relativistic covariance. A companion paper discusses the prospects for
combining a spacetime-based ontology with separability, along lines suggested
by Deutsch and HaydenComment: LaTeX; 29 pages, 1 Fig. Forthcoming in the British Journal for the
Philosophy of Scienc
Proper and Improper Separability
The distinction between proper and improper mixtures is a staple of the
discussion of foundational questions in quantum mechanics. Here we note an
analogous distinction in the context of the theory of entanglement. The
terminology of `proper' versus `improper' separability is proposed to mark the
distinction.Comment: 10 pages, LaTex, uses amsmath, 2 .eps figures. v2 additional figure;
and reference and footnote to Seevinck and Uffink (2001). To appear in
International Journal of Quantum Informatio
Entanglement and Relativity
In this paper we survey, in an elementary fashion, some of the questions that
arise when one considers how entanglement and relativity are related via the
notion of non-locality. We begin by reviewing the role of entangled states in
Bell inequality violation and question whether the associated notions of
non-locality lead to problems with relativity. The use of entanglement and
wavefunction collapse in Einstein's famous incompleteness argument is then
considered, before we go on to see how the issue of non-locality is transformed
if one considers quantum mechanics without collapse to be a complete theory, as
in the Everett interpretation. The opportunity is taken to consider whether
teleportation and dense coding might constitute a source of non-locality within
the Everett interpretation.Comment: 18 pages, uses amsmath, amsfonts, natbib and fancyheadings packages.
Typos corrected and additional referenc
Why special relativity should not be a template for a fundamental reformulation of quantum mechanics
In a comparison of the principles of special relativity and of quantum mechanics, the former theory is marked by its relative economy and apparent explanatory simplicity. A number of theorists have thus been led to search for a small number of postulates - essentially information theoretic in nature - that would play the role in quantum mechanics that the relativity principle and the light postulate jointly play in Einstein's 1905 special relativity theory. The purpose of the present paper is to resist this idea, at least in so far as it is supposed to reveal the fundamental form of the theory. It is argued that the methodology of Einstein's 1905 theory represents a victory of pragmatism over explanatory depth; and that its adoption only made sense in the context of the chaotic state state of physics at the start of the 20th century - as Einstein well knew
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