New test of the weak equivalence principle for neutrons

We describe a neutron gravity quantum experiment of a new type. The gain in kinetic energy of free-falling neutrons is compensated by a quantum of energy ℏ Ω , due to phase modulation of the neutron wave. As phase modulator a grating was used moving perpendicular with respect to the direction of the neutron wave propagation. As a result, monochromatic neutrons will have exactly the same energy after falling as before the free fall. The weak equivalence principle was tested to an accuracy of 2×10−3. A possible future experiment of more improved accuracy is discussed as well.