  A simple scheme to prepare an entanglement between two separated qubits from
a given mixed state is proposed. A single qubit (entanglement mediator) is
repeatedly made to interact locally and consecutively with the two qubits
through rotating-wave couplings and is then measured. It is shown that we need
to repeat this kind of process only three times to establish a maximally
entangled state directly from an arbitrary initial mixed state, with no need to
prepare the state of the qubits in advance or to rearrange the setup step by
step. Furthermore, the maximum yield realizable with this scheme is compatible
with the maximum entanglement, provided that the coupling constants are
properly tuned.
