Experimental Observation of the Drag Force Suppression in a Flow of Superfluid Light

We report a direct experimental detection of the frictional-superfluid transition in the flow of a fluid of light past a weakly perturbing localized obstacle in a bulk nonlinear crystal. In our cavityless all-optical system, we extract on the one hand a direct optical analog of the drag force experienced by the obstacle and measure on the other hand the associated obstacle displacement. We observe a superfluid regime characterized by a suppression of long-range radiation from the obstacle, which is, as expected, associated to the cancellation of the drag force and the absence of displacement of the obstacle