This article is cited in 24 papers

Information Theory

Classical capacities of quantum channels with environment assistance

S. Karumanchi^a, S. Mancini^bc, A. Winter^d, D. Yang<sup>de

a</sup> Faculty of Informatics, Masaryk University, Brno, Czech Republic
^b School of Science and Technology, University of Camerino, Camerino, Italy
^c INFN – Sezione Perugia, Perugia, Italy
^d ICREA and Física Teòrica: Informació i Fenòmens Quàntics, Universitat Autònoma de Barcelona, Barcelona, Spain
^e Laboratory for Quantum Information, China Jiliang University, Hangzhou, Zhejiang, China

Abstract: A quantum channel physically is a unitary interaction between an information carrying system and an environment, which is initialized in a pure state before the interaction. Conventionally, this state, as also the parameters of the interaction, is assumed to be fixed and known to the sender and receiver. Here, following the model introduced by us earlier [1], we consider a benevolent third party, i.e., a helper, controlling the environment state, and show how the helper's presence changes the communication game. In particular, we define and study the classical capacity of a unitary interaction with helper, in two variants: one where the helper can only prepare separable states across many channel uses, and one without this restriction. Furthermore, two even more powerful scenarios of pre-shared entanglement between helper and receiver, and of classical communication between sender and helper (making them conferencing encoders) are considered.

UDC: 621.391.1+519.7

Received: 23.09.2015
Revised: 03.02.2016

 English version: Problems of Information Transmission, 2016, 52:3, 214–238

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