Heralded and high-efficient entanglement concentrations based on linear optics assisted by time-delay degree of freedom

Entanglement concentration is a critical technique to prevent degraded fidelity and security in long-distance quantum communication. We propose novel practical entanglement concentration protocols (ECPs) for less-entangled Bell and Greenberger-Horne-Zeilinger states with unknown parameters by solely using simple linear optics. We avoid the need for the post-selection principles or photon-number-resolving detectors to identify the parity-check measurement completely by orchestrating auxiliary time degree of freedom, and the success of ECPs is exactly heralded by the detection signatures without destroying the incident qubits. Additionally, the outting incident photons kept are in the maximally entangled or the less-entangled state, and the success probability can be increased by recycling the latter. The heralded and the basic linear optical elements make our practical ECPs are accessible to experimental investigation with current technology. (c) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

Automated summary

In this study, we propose a novel entanglement concentration protocol based on simple linear optics, which can be used to concentrate less-entangled states with unknown parameters. Our protocol avoids the need for post-selection principles or photon-number-resolving detectors. By recycling the output photons, the success probability can be increased, and the experimental investigation can be easily conducted using basic linear optical elements.