I came across this article today and thought it looked interesting. https://www.simonsfoundation.org/quanta/20131107-physicists-eye-quantum-gravity-interface/ I believe experiments have maintained quantum superpositions across great distances over the surface of the earth. But does anyone know if they have done so over significant vertical distances? The article seems to suggest that gravity would destroy the entanglement. I can see why this must be the case, but I just wondered if there was evidence for it.