Antihydrogen Gravitational Quantum States
  We present a theoretical study of the motion of the antihydrogen atom ($\bar{H}$) in the Earth's gravitational field above a material surface. We predict that $\bar{H}$ atom, falling in the Earth's gravitational field above a material surface, would settle in long-living quantum states. We point out a method of measuring the difference in energy of $\bar{H}$ in such states that allow us to apply spectroscopy of gravitational levels based on atom-interferometric principles. We analyze a general feasibility to perform experiments of this kind. We point out that such experiments provide a method of measuring the gravitational force ($Mg$) acting on $\bar{H}$ and they might be of interest in a context of testing the Weak Equivalence Principle for antimatter. 
A.Yu. Voronin, P.Froelich, V.V. Nesvizhevsky
physics.atom-ph