2,452 research outputs found
Bell Correlations in Quantum Field Theory
Bell correlations are the hallmark of quantum non-locality, and a rich context for analysing them is provided by the algebraic approach to quantum field theory (AQFT): the basic idea is to associate with each bounded region O of Minkowski spacetime an algebra A(O) of operators, of which a self-adjoint element P ∈ A(O) represents a physical quantity pertaining to that part of the field system lying in O, that is measurable by a procedure confined to O. The violation of Bell inequalities in AQFT is known to be "generic", as regards the choices of regions O, and of quantities P, and of states. Furthermore, they are typically "maximal" and "indestructible" in a sense that can be made mathematically precise. The prospects for “peaceful coexistence” between quantum non-locality and relativity theory’s requirement of no action-at-a-distance are also explored. The purpose of this Essay is to review the developments in these areas
Characterizing common cause closedness of quantum probability theories
We prove new results on common cause closedness of quantum probability
spaces, where by a quantum probability space is meant the projection lattice of
a non-commutative von Neumann algebra together with a countably additive
probability measure on the lattice. Common cause closedness is the feature that
for every correlation between a pair of commuting projections there exists in
the lattice a third projection commuting with both of the correlated
projections and which is a Reichenbachian common cause of the correlation. The
main result we prove is that a quantum probability space is common cause closed
if and only if it has at most one measure theoretic atom. This result improves
earlier ones published in Z. GyenisZ and M. Redei Erkenntnis 79 (2014) 435-451.
The result is discussed from the perspective of status of the Common Cause
Principle. Open problems on common cause closedness of general probability
spaces are formulated, where is an
orthomodular bounded lattice and is a probability measure on
.Comment: Submitted for publicatio
Noncommutative Common Cause Principles in Algebraic Quantum Field Theory
States in algebraic quantum field theory "typically" establish correlation
between spacelike separated events. Reichenbach's Common Cause Principle,
generalized to the quantum field theoretical setting, offers an apt tool to
causally account for these superluminal correlations. In the paper we motivate
first why commutativity between the common cause and the correlating events
should be abandoned in the definition of the common cause. Then we show that
the Noncommutative Weak Common Cause Principle holds in algebraic quantum field
theory with locally finite degrees of freedom. Namely, for any pair of
projections A, B supported in spacelike separated regions V_A and V_B,
respectively, there is a local projection C not necessarily commuting with A
and B such that C is supported within the union of the backward light cones of
V_A and V_B and the set {C, non-C} screens off the correlation between A and B
Bell inequality and common causal explanation in algebraic quantum field theory
Bell inequalities, understood as constraints between classical conditional
probabilities, can be derived from a set of assumptions representing a common
causal explanation of classical correlations. A similar derivation, however, is
not known for Bell inequalities in algebraic quantum field theories
establishing constraints for the expectation of specific linear combinations of
projections in a quantum state. In the paper we address the question as to
whether a 'common causal justification' of these non-classical Bell
inequalities is possible. We will show that although the classical notion of
common causal explanation can readily be generalized for the non-classical
case, the Bell inequalities used in quantum theories cannot be derived from
these non-classical common causes. Just the opposite is true: for a set of
correlations there can be given a non-classical common causal explanation even
if they violate the Bell inequalities. This shows that the range of common
causal explanations in the non-classical case is wider than that restricted by
the Bell inequalities
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