Appearance of causality in process matrices when performing fixed-basis measurements for two parties

Author(s)
Veronika Baumann, Caslav Brukner
Abstract

The recently developed framework for quantum theory with no global causal order allows for quantum processes in which operations in local laboratories are neither causally ordered nor in a probabilistic mixture of definite causal orders. The causal relation between the laboratories is described by the process matrix. We show that, if the inputs of the laboratories are measured in a fixed basis, one can introduce an effective process matrix which is operationally indistinguishable from the original one. This effective process matrix can be obtained by applying the von Neumann-Lüders update rule for nonselective measurements to the original process matrix and, in the bipartite case, it is compatible with a definite causal order. The latter extends the original Oreshkov et al. proof where one considers that both the measurement of the input and the re-preparation of the output are performed in a fixed basis.

Organisation(s)
Quantum Optics, Quantum Nanophysics and Quantum Information
External organisation(s)
Università della Svizzera Italiana, Österreichische Akademie der Wissenschaften (ÖAW)
Journal
Physical Review A
Volume
93
No. of pages
3
ISSN
1050-2947
DOI
https://doi.org/10.1103/PhysRevA.93.062324
Publication date
06-2016
Peer reviewed
Yes
Austrian Fields of Science 2012
103025 Quantum mechanics
ASJC Scopus subject areas
Atomic and Molecular Physics, and Optics
Portal url
https://ucrisportal.univie.ac.at/en/publications/281fd72e-fc1b-4ac1-86c3-a071387d8ee1