325 research outputs found
On the symmetry of the seminal Horodecki state
It is shown that the seminal Horodecki 2-qutrit state belongs to the class of
states displaying symmetry governed by a commutative subgroup of the unitary
group U(3). Taking a conjugate subgroup one obtains another classes of
symmetric states and one finds equivalent representations of the Horodecki
state.Comment: 7 page
On exposed positive maps: Robertson and Breuer-Hall maps
It is well known that so called Breuer-Hall positive maps used in
entanglement theory are optimal. We show that these maps possess much more
subtle property --- they are exposed. As a byproduct it proves that a Robertson
map in the algebra of 4 x 4 complex matrices is not only extreme, which was
already shown by Robertson, but also exposed.Comment: 7 page
Circulant states with vanishing quantum discord
We analyze a class of 2-qudit circulant states. They define generalization of
well known 2-qubit X-states. We formula the necessary and sufficient criteria
for vanishing quantum discord. We illustrate our analysis by an important
subclass of circulant states -- so called Bell diagonal states.Comment: 8 page
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