  We derive an optimal bound for arbitrary entanglement manipulation based on
the transmission of a pulse in coherent states over a lossy channel followed by
local operations and unlimited classical communication (LOCC). This stands on a
theorem to reduce LOCC via a local unital qubit channel to local filtering. We
also present an optimal protocol based on beam splitters and a quantum
nondemolition (QND) measurement on photons. Even if we replace the QND
measurement with photon detectors, the protocol outperforms known entanglement
generation schemes.

Quantum Physics