Spectrometer for new gravitational experiment with UCN

We describe an experimental installation for a new test of the weak equivalence principle for neutron. The device is a sensitive gravitational spectrometer for ultracold neutrons allowing to precisely compare the gain in kinetic energy of free falling neutrons to quanta of energy ℏΩℏΩ transferred to the neutron via a non stationary device, i.e. a quantum modulator.The results of first test experiments indicate a collection rate allowing measurements of the factor of equivalence γ with a statistical uncertainty in the order of 5×10−3 per day. A number of systematic effects were found, which partially can be easily corrected. For the elimination of others more detailed investigations and analysis are needed. Some possibilities to improve the device are also discussed.