Quantum Test of the Universality of Free Fall
  We simultaneously measure the gravitationally-induced phase shift in two Raman-type matter-wave interferometers operated with laser-cooled ensembles of $^{87}$Rb and $^{39}$K atoms. Our measurement yields an E\"otv\"os ratio of $\eta_{\text{Rb,K}}=(0.3\pm 5.4)\times 10^{-7}$. We briefly estimate possible bias effects and present strategies for future improvements. 
Dennis Schlippert, Jonas Hartwig, Henning Albers, Logan L. Richardson,   Christian Schubert, Albert Roura, Wolfgang P. Schle...
physics.atom-ph gr-qc