Optical Galton board - art. no. 013410

The conventional Galton board illustrates diffusion in a classical-mechanic s context: it is composed of balls: performing a random walk on a downward sloping plane with a grid of pins. We introduce a wave-mechanical variety o f the Galton board to study the influence of interference on the diffusion. This variety consists of a wave, in our experiments a light wave, propagat ing through a grid of Landau-Zener crossings. At each crossing neighboring frequency levels are coupled, which leads to spectral diffusion of the init ial level populations. The most remarkable feature of the spectral diffusio n is that below a certain single-crossing transition probability (around 0. 7-0.8) the initial spectral distribution almost perfectly reappears periodi cally when the wave penetrates further and further into the grid of crossin gs. We compare our experimental results with numerical simulations and with an analytical description of the system based on a paper by Harmin [Phys. Rev. A 56, 232 (1997)].