Many-body entanglement swapping protocol: Opportunities for distributed quantum computing

Abstract

Sharing entangled pairs between nonsignaling parties via entanglement swapping constitutes a striking demonstration of the nonlocality of quantum mechanics and a crucial building block for future quantum technologies. In this work, we generalize pair-swapping methods by introducing a many-body entanglement swapping protocol, which allows two nonsignaling parties to share general many-body states along an arbitrary partitioning. The shared many-body state retains exactly the same Schmidt vectors as the target state and exhibits typically high fidelity, which approaches unity as the variance of the Schmidt coefficients vanishes. Moreover, we demonstrate how the three-party protocol can be generalized to many-body swapping networks, enabling a general many-body state sharing with unit fidelity via arbitrary number of intermediate nodes. This is achieved by replacing all but one of the unitary operations with those corresponding to the same Schmidt states but with a flattened spectrum, which also completely eliminates the need for postselection. We provide a proof of concept of the three-party protocol on real quantum hardware and discuss how it enables functionalities, such as fault-tolerant entanglement swapping and strategies for distributed quantum computing.