Entanglement concentration of W state using linear optics with a higher success probability

Entanglement concentration protocol (ECP), as a practical technique, can be use to preclude degraded fidelity and improve security in long-haul quantum communication. We propose an efficient ECP for less-entangled unknown W states with simple linear-optics elements and effective single-photon detectors, resorting to time-delay degree of freedom. Moreover, in contrast to previous ECPs proposed for W states, the scheme has the advantages over requiring less quantum resource without auxiliary photons, comparatively simplified circuits, involving neither post-selection techniques nor photon-number-resolving detectors to distinguish the parity outcome, and being provided with a higher success probability by reusing the less-entangled states.