Entanglement-redistribution boxes

We establish a framework to study the classical-communication properties of primitive local operations assisted by classical communication which realize various redistributions of entanglement, like, e.g., entanglement swapping. On the one hand, we analyze what local operations and how much classical communication are needed to perform them. On the other hand, we investigate whether and to what extent such primitives can help to establish classical communication when they are used in the form of black boxes available to spatially separated users. In particular, we find that entanglement swapping costs more communication than it can signal; in this sense, entanglement swapping is a weaker primitive than quantum teleportation.

Figure 1

Entanglement swapping (continuous arrow) in two steps (dashed arrows): from two EPR pairs to a GHZ state, to the final EPR pair. Lines denote quantum correlations.

Figure 2

Entanglement swapping (black) box.