Can a single-pulse standing wave induce chaos in atomic motion?

We measure momentum transferred from a single pulse of a standing wave of light to a sample of ultracold sodium atoms, and observe a sharp increase in the momentum transfer when the pulse duration exceeds a critical value τcr. A classical analysis of nonlinear resonances shows that resonance overlap occurs at τcr, and there is a transition to global classical chaos. These results are a direct experimental test of the open-quote open-quote resonance overlap criteria close-quote close-quote and illustrate that even the turning on and off of a simple spatially periodic interaction can lead to surprising and novel results. copyright 1996 The American Physical Society