Gravitationally bound quantum states of ultracold neutrons and their applications

We will review the discovery and characterization of gravitationally bound quantum states of neutrons. The lowest neutron quantum states in a gravitational potential were distinguished and characterized by a measurement of their spatial extent. The neutron transmission was observed through a slit with an absorbing top surface at a variable height. Second, a position-sensitive detector was used for a direct visualization of the wavefunction. An application is the search for new short-range interactions, which would alter the waveform of the quantum states.