Boosted Entanglement Swapping

arXiv:2611.05497v1 Announce Type: new Abstract: Entanglement swapping entangles photons that never interacted directly. When implemented with linear optics, its success probability is upper bounded by $50\%$, due to the limited efficiency of linear-optical Bell-state measurements. Here, we demonstrate boosted entanglement swapping using an ancilla-assisted linear-optical Bell-state measurement, which raises the theoretical success probability to $62.5\%$ and allows all four Bell states to be identified. We measure an acceptance rate of $p_{\mathrm{a}}^{\mathrm{b}}=(69.39\pm0.39)\%$ with an average fidelity of the swapped states of $\langle F^{\mathrm{b}}\rangle=(76.6\pm1.0)\%$.