Optimal multi-photon entanglement concentration with the photonic Faraday rotation

We put forward an optimal entanglement concentration protocol (ECP) for recovering an arbitrary less-entangled multi-photon Greenberger-Horne-Zeilinger (GHZ) state into the maximally entangled GHZ state based on the photonic Faraday rotation in low-quality (Q) cavity. In the ECP, only one pair of less-entangled multi-photon GHZ state and one auxiliary photon are required, and the concentration task can be realized by local operations. Moreover, our ECP can be used repeatedly to further concentrate the discarded items of conventional ECPs, which can increase its success probability largely. Under the practical imperfect detection condition, our protocol can still work with relatively high success probability. This ECP has application potential in current and future quantum communication.