515 research outputs found
Bipartite Bell inequalities for hyperentangled states
We show that bipartite Bell inequalities based on the Einstein-Podolsky-Rosen
criterion for elements of reality and derived from the properties of some
hyperentangled states allow feasible experimental verifications of the fact
that quantum nonlocality grows exponentially with the size of the subsystems,
and Bell loophole-free tests with currently available photodetection
efficiencies.Comment: REVTeX4, 5 page
Hyperentangled States
We investigate a new class of entangled states, which we call
'hyperentangled',that have EPR correlations identical to those in the vacuum
state of a relativistic quantum field. We show that whenever hyperentangled
states exist in any quantum theory, they are dense in its state space. We also
give prescriptions for constructing hyperentangled states that involve an
arbitrarily large collection of systems.Comment: 23 pages, LaTeX, Submitted to Physical Review
Modelling a Particle Detector in Field Theory
Particle detector models allow to give an operational definition to the
particle content of a given quantum state of a field theory. The commonly
adopted Unruh-DeWitt type of detector is known to undergo temporary transitions
to excited states even when at rest and in the Minkowski vacuum. We argue that
real detectors do not feature this property, as the configuration "detector in
its ground state + vacuum of the field" is generally a stable bound state of
the underlying fundamental theory (e.g. the ground state-hydrogen atom in a
suitable QED with electrons and protons) in the non-accelerated case. As a
concrete example, we study a local relativistic field theory where a stable
particle can capture a light quantum and form a quasi-stable state. As
expected, to such a stable particle correspond energy eigenstates of the full
theory, as is shown explicitly by using a dressed particle formalism at first
order in perturbation theory. We derive an effective model of detector (at
rest) where the stable particle and the quasi-stable configurations correspond
to the two internal levels, "ground" and "excited", of the detector.Comment: 13 pages, references added, final versio
Quantum mechanics and elements of reality inferred from joint measurements
The Einstein-Podolsky-Rosen argument on quantum mechanics incompleteness is
formulated in terms of elements of reality inferred from joint (as opposed to
alternative) measurements, in two examples involving entangled states of three
spin-1/2 particles. The same states allow us to obtain proofs of the
incompatibility between quantum mechanics and elements of reality.Comment: LaTeX, 12 page
Generic Bell correlation between arbitrary local algebras in quantum field theory
We prove that for any two commuting von Neumann algebras of infinite type,
the open set of Bell correlated states for the two algebras is norm dense. We
then apply this result to algebraic quantum field theory -- where all local
algebras are of infinite type -- in order to show that for any two spacelike
separated regions, there is an open dense set of field states that dictate Bell
correlations between the regions. We also show that any vector state cyclic for
one of a pair of commuting nonabelian von Neumann algebras is entangled (i.e.,
nonseparable) across the algebras -- from which it follows that every field
state with bounded energy is entangled across any two spacelike separated
regions.Comment: Third version; correction in the proof of Proposition
Neurology
Contains reports on five research projects.United States Navy, Office of Naval Research (Nonr-609(39))United States Public Health Service (B-3055, B-3090)Unites States Air Force (Contract AF33(616)-7282)Unites States Air Force (Contract AF-33(616)-7588, Project: 61(8-7232); Task 71784))United States Army Chemical Corps (DA-18-108-405-Cml-942
Neurology
Contains reports on six research projects.Public Health Service (B-3055, B-3090)United States Air Force (AF33(616)-7282, AF49(638)-1130)United States Navy, Office of Naval Research (Nonr-609(39))United States Army Chemical Corps (DA-18-108-405-Cml-942)National Science Foundation (Grant G-16526
Consistent Resolution of Some Relativistic Quantum Paradoxes
A relativistic version of the (consistent or decoherent) histories approach
to quantum theory is developed on the basis of earlier work by Hartle, and used
to discuss relativistic forms of the paradoxes of spherical wave packet
collapse, Bohm's formulation of Einstein-Podolsky-Rosen, and Hardy's paradox.
It is argued that wave function collapse is not needed for introducing
probabilities into relativistic quantum mechanics, and in any case should never
be thought of as a physical process. Alternative approaches to stochastic time
dependence can be used to construct a physical picture of the measurement
process that is less misleading than collapse models. In particular, one can
employ a coarse-grained but fully quantum mechanical description in which
particles move along trajectories, with behavior under Lorentz transformations
the same as in classical relativistic physics, and detectors are triggered by
particles reaching them along such trajectories. States entangled between
spacelike separate regions are also legitimate quantum descriptions, and can be
consistently handled by the formalism presented here. The paradoxes in question
arise because of using modes of reasoning which, while correct for classical
physics, are inconsistent with the mathematical structure of quantum theory,
and are resolved (or tamed) by using a proper quantum analysis. In particular,
there is no need to invoke, nor any evidence for, mysterious long-range
superluminal influences, and thus no incompatibility, at least from this
source, between relativity theory and quantum mechanics.Comment: Latex 42 pages, 7 figures in text using PSTrick
Quasi-probability representations of quantum theory with applications to quantum information science
This article comprises a review of both the quasi-probability representations
of infinite-dimensional quantum theory (including the Wigner function) and the
more recently defined quasi-probability representations of finite-dimensional
quantum theory. We focus on both the characteristics and applications of these
representations with an emphasis toward quantum information theory. We discuss
the recently proposed unification of the set of possible quasi-probability
representations via frame theory and then discuss the practical relevance of
negativity in such representations as a criteria for quantumness.Comment: v3: typos fixed, references adde
The Possibilist Transactional Interpretation and Relativity
A recent ontological variant of Cramer's Transactional Interpretation, called
"Possibilist Transactional Interpretation" or PTI, is extended to the
relativistic domain. The present interpretation clarifies the concept of
'absorption,' which plays a crucial role in TI (and in PTI). In particular, in
the relativistic domain, coupling amplitudes between fields are interpreted as
amplitudes for the generation of confirmation waves (CW) by a potential
absorber in response to offer waves (OW), whereas in the nonrelativistic
context CW are taken as generated with certainty. It is pointed out that
solving the measurement problem requires venturing into the relativistic domain
in which emissions and absorptions take place; nonrelativistic quantum
mechanics only applies to quanta considered as 'already in existence' (i.e.,
'free quanta'), and therefore cannot fully account for the phenomenon of
measurement, in which quanta are tied to sources and sinks.Comment: Final version with some minor corrections as published in Foundations
of Physics. This paper has significant overlap with Chapter 6 of my book on
the Transactional Interpretation, forthcoming from Cambridge University
Press:
http://www.cambridge.org/us/knowledge/isbn/item6860644/?site_locale=en_US
(Additional preview material is available at rekastner.wordpress.com)
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