  We propose a scheme for both distilling and quantifying entanglement,
applicable to individual copies of an arbitrary unknown two-qubit state. It is
realized in a usual two-qubit interferometry with local filtering. Proper
filtering operation for the maximal distillation of the state is achieved, by
erasing single-qubit interference, and then the concurrence of the state is
determined directly from the visibilities of two-qubit interference. We compare
the scheme with full state tomography.
