Hi all,
today we'll hear from Ognyan Oreshkov, visiting from Brussels. The title
and abstract of his talk follow below.
Best,
-joe
Title:
Quantum theory with indefinite causal structure
Abstract:
Quantum theory can be understood as a theory of information processing
in the circuit framework for operational probabilistic theories. This
approach presupposes a definite casual structure as well as a
preferred time direction. But in general relativity, the causal
structure of space-time is dynamical and not predefined. This
indicates that a quantum theory that could incorporate gravity
requires a more general operational paradigm. In this talk, I will
describe recent progress in this direction. First, I will explain how
relaxing the assumption that local operations take place in a global
causal structure leads to a generalized framework that unifies all
signaling and non-signaling quantum correlations in space-time via an
extension of the density matrix called the process matrix. This
framework also contains correlations incompatible with any definite
causal structure, which violate causal inequalities, the general
theory of which I am going to present. I will then present an
extension of the process matrix framework, in which no predefined
causal structure is assumed even locally. This is based on a more
general, time-neutral notion of operation, which leads to new insights
into the problem of time-reversal symmetry in quantum mechanics, the
meaning of causality, and the fact that we remember the past but not
the future. In the resultant generalized formulation of quantum
theory, operations are associated with regions that can be connected
in networks with no directionality assumed for the connections. The
theory is compatible with timelike loops and other acausal structures.