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.