We report a direct experimental detection of the frictional-superfluidtransition in the flow of a fluid of light past a weakly perturbing localizedobstacle in a bulk nonlinear crystal. In our cavityless all-optical system, weextract on the one hand a direct optical analog of the drag force experiencedby the obstacle and measure on the other hand the associated obstacledisplacement. We observe a superfluid regime characterized by a suppression oflong-range radiation from the obstacle, which is, as expected, associated tothe cancellation of the drag force and the absence of displacement of theobstacle.
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