November, 23 (2007) at 4:30pm

Julio de Vicente
Universidad Carlos III de Madrid

Entanglement plays a central role in Quantum Information Theory as well as inthe foundations of Quantum Mechanics. Thus, it is crucial to be able todecide wether or not a given quantum state is entangled. However, and despite many advances in the last decade, this so-called separability problem remains open. In this talk I will present new separability criteria obtained by approaching the problem using the Bloch representation of density matrices. In particular, this includes a powerful sufficient condition for the presence of entanglement, which Iwill show is strong enough to detect entangled states which are notrecognized by previous important criteria. Interestingly, theexperimental implementation of this condition relies on the measurement of some particular correlations which can be done locally and requires less effort than the explicit determination of the state. Finally, I will also show that this condition not only helps to detect entanglement, but can also be used to estimate the amount of entanglement present in a quantum state. This is because a relation can be established between the measure on which this condition relies and the entanglement measure known as concurrence. In particular, we are able to derive lower bounds for the concurrence.