Open system dynamics of simple collision models

TL;DR

This paper uses simple collision models to explore open quantum system dynamics, including thermalization, decoherence, and entanglement generation, and derives related master equations.

Contribution

It introduces quantum homogenization and decoherence collision models, linking discrete collisions to Lindblad master equations, and demonstrates their use in generating multipartite entangled states.

Findings

Collision models simulate quantum thermalization and decoherence.

Partial swaps produce W-type entanglement.

Decoherence collisions create GHZ-type entanglement.

Abstract

A simple collision model is employed to introduce elementary concepts of open system dynamics of quantum systems. In particular, within the framework of collision models we introduce the quantum analogue of thermalization process called quantum homogenization and simulate quantum decoherence processes. These dynamics are driven by partial swaps and controlled unitary collisions, respectively. We show that collision models can be used to prepare multipartite entangled states. Partial swap dynamics generates W-type of entanglement saturating the CKW inequalities, whereas the decoherence collision models creates GHZ-type of entangled states. The considered evolution of a system in a sequence of collisions is described by a discrete semigroup E_1,...,E_n. Interpolating this discrete points within the set of quantum channels we derive for both processes the corresponding Lindblad master equations. In particular, we argue that collision models can be used as simulators of arbitrary Markovian dynamics, however, the inverse is not true.