Even more recently, the model used to demonstrate superradiance and subradiance in a bipartite system of walking droplets, was extended to produce the first hydrodynamic static Bell test. In this test, the two two-level systems, which are spatially separated by the intermediate deep region, are subjected to tunable measurement settings and their correlation functions are evaluated by repeating measurement cycles. These alternating measurement settings only substantially affect the local tunneling probabilities when the system is uncoupled, or weakly coupled. However, in a strongly-coupled system, each local setting does affect the global tunneling behavior. The static Bell inequality is a measure of how strongly coupled this system can be in terms of its collective behavior, and we have found that at specific parameter regimes the Bell inequality is violated by such bipartite systems of walking droplets. We are currently assessing this violation in terms of its physical meaning, the potential to explore more elaborate hydrodynamic Bell tests, their experimental extensions and potential practical applications.
Ref: K Papatryfonos, L Vervoort, A Nachbin, M Labousse, JWM Bush Bell test in a classical pilot-wave system arXiv:2208.08940v1 [preprint]