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Measures of entanglement for two-mode Gaussian states
  KTH/Nordita/SU seminar in Theoretical Physics [before December 2013]

Tuesday 02 June 2009
from 13:15 to 14:15
at FA32 (OBS!)
Speaker : Paulina Marian (Bucharest)
Abstract : For a long time Gaussian states of the quantum radiation field are known to be of central importance in various areas of quantum optics. In general, such quantum states play a conspicuous role for those systems involving a quadratic bosonic Hamiltonian that generates correlations between bosonic modes. They are achieved in condensed matter, as well as in atomic ensembles such as trapped ions or Bose-Einstein condensates. The Gaussian states of light are also largely employed in quantum information processing with continuous variables. Recent developments in the theory of quantum information focused on a deeper understanding of the properties of entangled states. Several measures of entanglement have been considered for mixed bipartite states. Due to its operational meaning, one of the most promising is the entanglement of formation (EF) defined as the minimal entanglement of any ensemble of pure bipartite states realizing the given mixed state. Our aproach to EF for Gaussian states is based on concepts currently used in quantum optics, such as characteristic functions, P-representativity and field superpositions. Combined with a more abstract description of Gaussian states based on the properties of their covariance matrices, we give an essentially physical approach to a very complicated mathematical task, namely, the extremization problem of EF. We then show that EF is consistent to another measure of entanglement: the Bures distance between the given entangled Gaussian state and the set of all separable states.

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