Open-System Dynamics of Entanglement

One of the greatest challenges in quantum information processing is the coherent control over quantum systems with an ever increasing number of particles. Within this endeavor, the harnessing of many-body entanglement against the effects of the environment is a pressing issue. Besides being an important concept from a fundamental standpoint, entanglement is recognized as a crucial resource for performance enhancements over classical methods. Understanding and controlling many-body entanglement in open systems may have implications in quantum computing, quantum simulations, secure quantum communication, quantum metrology, our understanding of the quantum-to-classical transition, and other important questions of quantum foundations. Here we present an overview of recent theoretical and experimental efforts to underpin the dynamics of entanglement in open quantum systems. Entanglement is taken as a dynamic quantity, and we survey how it evolves due to the interaction of the entangled system with its surroundings. We analyze several scenarios, corresponding to different families of states and environments, which render a diversity of dynamical behaviors. Contrary to single-particle quantities, that typically vanish only asymptotically in time, entanglement may disappear at a finite time. Moreover, important classes of entanglement show an exponential decay with the system size when subject to local noise, posing yet another threat to the already challenging scaling of quantum technologies. Results for the local and global noise cases are summarized. Robustness-enhancement techniques, scaling laws, statistical and geometrical aspects of multipartite-entanglement decay are also reviewed; all in order to give a broad picture of entanglement dynamics in open quantum systems addressed to both theorists and experimentalists inside and outside the field of quantum information.

Scalability of GHZ and random-state entanglement in the presence of decoherence

We derive analytical upper bounds for the entanglement of generalized Greenberger-Horne-Zeilinger states coupled to locally depolarizing and dephasing environments, and for local thermal baths of arbitrary temperature. These bounds apply for any convex quantifier of entanglement, and exponential entanglement decay with the number of constituent particles is found. The bounds are tight for depolarizing and dephasing channels. We also show that randomly generated initial states tend to violate these bounds, and that this discrepancy grows with the number of particles.