Atoms that move from one optical lattice site to another under laser-assisted tunneling circle through the sites, as in figure 3b. (a) One experiment measured the center-of-mass positions of atoms (dots) <x> and <y>, scaled to the lattice constants dx and dy, as the atoms move among the four sites (inset) over 2.1 ms. (Adapted from ref. 9.) (b) In another experiment, the positions (dots) of BEC atoms are mapped along the edges of a long, thin virtual strip. The horizontal dimension, scaled to the lattice constants, is real, and the narrow dimension is synthetic, formed by the atoms’ spin states 1, 0, and −1. The edge currents to the left (pink) and right (blue) evolve in time with opposite velocities and are the result of the “skipping orbits,” in which the atoms mimic cyclotron motion and periodically reflect from the strip’s edges. (Adapted from ref. 13.)