KTH/Nordita/SU seminar in Theoretical Physics [before December 2013]

Wednesday 21 February 2007
from 11:00
to 12:00 at
AlbaNova
(
FB41
)

Speaker :

Piotr Badziag (SU)

Abstract :

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.