Remote preparation of $W$ states from imperfect bipartite sources

TL;DR

This paper presents a deterministic protocol for remotely generating $W$ states from an EPR source, demonstrating robustness against source imperfections and enabling entanglement concentration and lifting.

Contribution

It introduces a novel, measurement-based method to produce $W$ states remotely from imperfect bipartite sources, improving reliability and fidelity.

Findings

Protocol remains effective with source flaws after postselection.

Resulting mixed states have higher fidelity than the original imperfect sources.

The method enables entanglement concentration and lifting even with imperfections.

Abstract

Several proposals to produce {\it tripartite} $W$-type entanglement are probabilistic even if no imperfections are considered in the processes. We provide a deterministic way to remotely create $W$ states out of an EPR source. The proposal is made viable through measurements (which can be demolitive) in an appropriate three-qubit basis. The protocol becomes probabilistic only when source flaws are considered. It turns out that, even in this situation, it is robust against imperfections in two senses: (i) It is possible, after postselection, to create a pure ensemble of $W$ states out of an EPR source containing a systematic error; (ii) If no postselection is done, the resulting mixed state has a fidelity, with respect to a pure $|W\rangle$, which is higher than that of the imperfect source in comparison to an ideal EPR source. This simultaneously amounts to entanglement concentration and {\it lifting}.