Multistage Entanglement Swapping

TL;DR

This paper demonstrates a multistage entanglement swapping experiment using three photon pairs, successfully entangling photons from independent sources through cascaded Bell-state measurements, advancing quantum repeater development.

Contribution

It provides the first experimental realization of multistage entanglement swapping with independent photon sources, crucial for scalable quantum communication.

Findings

Entanglement was successfully swapped over two stages.

Photons from independent sources were entangled without shared history.

The experiment advances quantum repeater technology.

Abstract

We report an experimental demonstration of entanglement swapping over two quantum stages. By successful realizations of two cascaded photonic entanglement swapping processes, entanglement is generated and distributed between two photons, that originate from independent sources and do not share any common past. In the experiment we use three pairs of polarization entangled photons and conduct two Bell-state measurements (BSMs) one between the first and second pair, and one between the second and third pair. This results in projecting the remaining two outgoing photons from pair 1 and 3 into an entangled state, as characterized by an entanglement witness. The experiment represents an important step towards a full quantum repeater where multiple entanglement swapping is a key ingredient.