Of Local Operations and Physical Wires. (arXiv:1802.02021v1 [quant-ph])

In this work (multipartite) entanglement, discord and coherence are unified
as different aspects of a single underlying resource theory defined through
simple and operationally meaningful elemental operations. This is achieved by
revisiting the resource theory defining entanglement, Local Operations and
Classical Communication (LOCC), placing the focus on the underlying quantum
nature of the communication channels. Taking the natural elemental operations
in the resulting generalization of LOCC yields a resource theory that singles
out coherence in the wire connecting the spatially separated systems as an
operationally useful resource. The approach naturally allows to consider a
reduced setting as well, namely the one with only the wire connected to a
single quantum system, which leads to discord-like resources. The general form
of free operations in this latter setting is derived and presented as a closed
form. We discuss in what sense the present approach defines a resource theory
of quantum discord and in which situations such an interpretation is sound --
and why in general discord is not a resource. This unified and operationally
meaningful approach makes transparent many features of entanglement that in
LOCC might seem surprising, such as the possibility to use a particle to
entangle two parties, without it ever being entangled with either of them, or
that there exist different forms of multipartite entanglement.

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