Experimental recycling of Bell nonlocality with projective measurements

TL;DR

This paper experimentally demonstrates that projective measurements can recycle Bell nonlocality among three independent parties, challenging previous beliefs and enabling more practical quantum resource reuse without entanglement assistance.

Contribution

It provides the first experimental evidence that projective measurements can be used for recycling Bell nonlocality, expanding the scope beyond unsharp measurements.

Findings

Three parties can recycle nonlocality from a two-qubit state.

Partially entangled states show an 11 standard deviation better trade-off.

Recycling does not require entanglement assistance, simplifying experiments.

Abstract

As a way of saving quantum resources, recycling of Bell nonlocality has been experimentally studied, but restricted to sequential unsharp measurements. However, it has been theoretically shown recently that projective measurements are sufficient for recycling nonlocality [Phys. Rev. Lett. \textbf{129}, 230402 (2022)]. Here, we go beyond unsharp measurement scenarios and experimentally demonstrate the recycling of nonlocal resources with projective measurements. By verifying the violation of Clauser-Horne-Shimony-Holt (CHSH) inequality, we find that three independent parties can recycle the Bell nonlocality of a two-qubit state, whether it is maximally or partially entangled. Furthermore, in the double violation region, the optimal trade-off for partially entangled states can be 11 standard deviations better than that for maximally entangled states. Our results experimentally eliminate the common misconception that projective measurements are incompatible with the recycling of quantum correlations. In addition, our nonlocality recycling setup does not require entanglement assistance, which is much more experimentally friendly, thus paving the way for the reuse of other kinds of quantum correlations.