Atomic Interferometer with Amplitude Gratings of Light and its   Applications to Atom Based Tests of the Equivalence Principle
  We have developed a matter wave interferometer based on the diffraction of atoms from effective absorption gratings of light. In a setup with cold rubidium atoms in an atomic fountain the interferometer has been used to carry out tests of the equivalence principle on an atomic basis. The gravitational acceleration of the two isotopes 85Rb and 87Rb was compared, yielding a difference Dg/g =(1.2 +-1.7)x10^{-7}. We also perform a differential free fall measurement of atoms in two different hyperfine states, and obtained a result of Dg/g =(0.4 +-1.2)x10^{-7}. 
Sebastian Fray, Cristina Alvarez Diez, Theodor W. H\"ansch and Martin   Weitz