Abstract
The quantum mechanical propagator of a massive particle in a linear gravitational potential derived already in 1927 by Earle H. Kennard \cite{Kennard,Kennard2} contains a phase that scales with the third power of the time T during which the particle experiences the corresponding force. Since in conventional atom interferometers the internal atomic states are all exposed to the same acceleration a, this T³-phase cancels out and the interferometer phase scales as T². In contrast, by applying an external magnetic field we prepare two different accelerations a₁ and a₂ for two internal states of the atom, which translate themselves into two different cubic phases and the resulting interferometer phase scales as T³. We present the theoretical background for, and summarize our progress towards experimentally realizing such a novel atom interferometer.