DF Seminar

[Rosita Glavina]

Department of Physics - University of Trieste

Informal Seminar

Thursday 14 January 2010 - 15.00 hrs.
Room 204 (2nd floor, LB) 

Marco PIANI
(Institute for Quantum Computing - University of Waterloo, Canada)

USEFULNESS OF ENTANGLEMENT IN CHANNEL DISCRIMINATION
WITH AND WITHOUT RESTRICTED MEASUREMENTS

Abstract:
The usefulness of entanglement in minimum-error channel discrimination
is addressed. Firstly, we prove that, given a single copy of an
arbitrary bipartite entangled state, it holds that there is an
instance of a quantum channel discrimination task for which this state
allows for a correct discrimination with strictly higher probability
than every separable state. Secondly, we study the consequences of
restrictions on the measurements allowed in the discrimination
procedure. Operationally defined norms on super-operators (in
particular, a "weakened" version of the diamond norm) are
introduced. It is shown that there are pairs of channels for which a
restriction on the allowed measurements on the output of the
channel (e.g., to measurements performed by local operations and
classical communication) makes the use of an entangled input no more
powerful than a discrimination not based on the use of entanglement.
On the other hand, there are pairs of channels for which the use of an
entangled input remains advantageous despite the restriction on the
output measurement.