Observable estimation of entanglement for arbitrary finite-dimensional mixed states

Abstract

We present observable upper bounds for the squared concurrence, which are the dual inequalities of the observable lower bounds introduced by Mintert and Buchleitner [Phys. Rev. Lett. 98, 140505 (2007)] and Aolita et al. [Phys. Rev. A 78, 022308 (2008)]. These bounds can be used to estimate entanglement for arbitrary experimental unknown finite-dimensional states by a few experimental measurements on a twofold copy $\rho \otimes \rho$ of the mixed states. Furthermore, the degree of mixing for a mixed state and some properties of the linear entropy also have certain relations with the upper and lower bounds of its squared concurrence.