1012.3075 (J. Maziero et al.)

Classicality witness for two-qubit states    [PDF]

J. Maziero, R. M. Serra

In the last few years one realized that if the state of a bipartite system
can be written as $\sum_{i,j}p_{ij}|a_{i}>< a_{i}|\otimes |b_{j}> < b_{j}|$,
where $\{|a_{i}> \}$ and $\{|b_{j}> \}$ form orthonormal basis for the
subsystems and $\{p_{ij}\}$ is a probability distribution, then it possesses at
most classical correlations. In this article we introduce a nonlinear witness
providing a sufficient condition for classicality of correlations (absence of
quantum discord) in a broad class of two-qubit systems. Such witness turns out
to be necessary and sufficient condition in the case of Bell-diagonal states.
We show that the witness introduced here can be readily experimentally
implemented in nuclear magnetic resonance setups.

View original: http://arxiv.org/abs/1012.3075