  Multipartite quantum systems show properties which do not admit a classical
explanation. In particular, even nonentangled states can enjoy a kind of
quantum correlations called quantum discord. I discuss some recent results on
the role of quantum discord in metrology. Given an interferometric phase
estimation protocol where the Hamiltonian is initially unknown to the
experimentalist, the quantum discord of the probe state quantifies the minimum
precision of the estimation. This provides a physical interpretation to a
widely investigated information-theoretic quantity.
