8:30 AM-9:30 AM
Room: Ballrooms I, II & III
Chair: Steven H. Strogatz, Cornell University
Quantum atoms interact with light through a spatially-varying sinusoidal potential. This diffracts the atoms into a series of Bragg beams (previously studied for the diffraction of light by ultrasound). For real (nondissipative) potentials, classical motion is integrable; nevertheless, the semiclassical limit for thick crystals is ergodic, and caustics give large "twinkling" fluctuations. The potential can be made arbitrarily complex by adjusting the detuning. If it is purely imaginary, diffraction reveals nonhermitian degeneracies of the Bloch waves, and the distribution of intensities is dominated by complex rays rather than caustics. For complex potentials proportional to exp(iKx), the intensities can be calculated exactly, giving lopsided diffraction -- and a dramatic violation of Friedel's law of crystallography, even a fractal.
Sir Michael Berry
H. H. Wills Physics Laboratory
University of Bristol, United Kingdom
MMD, 2/9/99