KTH/Nordita/SU seminar in Theoretical Physics

Revisiting the separability problem

by Piotr Badziag (SU)

Europe/Stockholm
FB41 (AlbaNova)

FB41

AlbaNova

Description
To check separability of an arbitrary bipartite quantum state \varrho is a difficult task. It is equivalent to an axhaustive search over the set of all entanglement witnesses and the operational structure of this set is not known so far. In an attempt to overcome some of the difficulties, in the talk I will translate the separability problem into a characterization of a single witness operator. More specifically, I will show that state \varrho is separable if and only if an entanglement witness W_{\varrho} constructed out of a pure state decomposition of \varrho is "tangent" to the set of separable states, i.e., its expectation value vanishes on at least one product vector. As a byproduct, this approach provides an automatic method for construction of a class of entanglement witnesses.