  We derive measurable lower bounds on concurrence of arbitrary mixed states,
for both bipartite and multipartite cases. First, we construct measurable lower
bonds on the purely algebraic bounds of concurrence [F. Mintert et al. (2004),
Phys. Rev. lett., 92, 167902]. Then, using the fact that the sum of the square
of the algebraic bounds is a lower bound of the squared concurrence, we sum
over our measurable bounds to achieve a measurable lower bound on concurrence.
With two typical examples, we show that our method can detect more entangled
states and also can give sharper lower bonds than the similar ones.

Quantum Physics