Fringe Visibility and Which-Way Information in an Atom Interferometer

We experimentally investigate the reduction of the fringe visibility in an atom interferometer due to the storage of which-way information. We focus on the case of incomplete which-way information and use the distinguishability $D$ to quantify how much information is stored. For a given value of $D$, the fringe visibility $V$ is limited by the duality relation $D^2{+V}^2\le 1$. We have measured $D$ and $V$ independently. Combining the results, we find good agreement with the duality relation.