Structure of states for which each localized dynamics reduces to a localized subdynamics

Abstract

We consider a bipartite quantum system [Formula: see text] (including parties [Formula: see text] and [Formula: see text]), interacting with an environment [Formula: see text] through a localized quantum dynamics [Formula: see text]. We call a quantum dynamics [Formula: see text] localized if, e.g. the party [Formula: see text] is isolated from the environment and only [Formula: see text] interacts with the environment: [Formula: see text], where [Formula: see text] is the identity map on the part [Formula: see text] and [Formula: see text] is a completely positive (CP) map on the both [Formula: see text] and [Formula: see text]. We will show that the reduced dynamics of the system is also localized as [Formula: see text], where [Formula: see text] is a CP map on [Formula: see text], if and only if the initial state of the system-environment is a Markov state. We then generalize this result to the two following cases: when both [Formula: see text] and [Formula: see text] interact with a same environment, and when each party interacts with its local environment.