Keldysh formalism for multiple parallel worlds

TL;DR

This paper reviews the Keldysh formalism extended to multiple parallel worlds, enabling quantum evaluation of informational flows like Renyi and Shannon entropy, with a focus on the formalism and its applications.

Contribution

It introduces a compact, self-contained review of the extended Keldysh formalism for multiple worlds and demonstrates its application to quantum informational flow evaluations.

Findings

Formalism successfully applied to entropy flow calculations

Provides a unified framework for multiple parallel worlds

Summarizes concrete results obtained with the method

Abstract

We present here a compact and self-contained review of recently developed Keldysh formalism for multiple parallel worlds. The formalism has been applied to consistent quantum evaluation of the flows of informational quantities, in particular, to evaluation of Renyi and Shannon entropy flows. We start with the formulation of standard and extended Keldysh technique in single world in a form convenient for our presentation. We explain the use of Keldysh contours encompassing multiple parallel worlds In the end, we shortly summarize the concrete results obtained with the method.