This video showcases the diffraction of walking droplets by a standing Faraday wave. This system represents a hydrodynamic analogue of the Kapitza-Dirac effect, in which matter is diffracted by light. A millimetric droplet placed on a vertically vibrated bath may self-propel through a resonant interaction with its own wave field, providing a macroscopic example of wave-particle duality of the form proposed for quantum systems by Louis de Broglie a century ago. When the droplets cross the standing wave field, they are steered into discrete channels aligned with the wave extrema. The ensemble of trajectories form a coherent diffraction pattern reminiscent of that arising when electrons are diffracted by a standing electromagnetic wave.
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