In a potential of this type, transitions between states can be suppressed by tuning the potential to the “magic wavelength.” In a potential of this type, the ratio between an interaction matrix element, U, and a tunneling parameter, J, has a critical value denoting a phase transition. Rubidium atoms in a potential of this type transition between superfluid and Mott insulator states as the potential depth is increased. An alternative to the fountain method for making atomic clocks involves a potential of this type which traps atoms using the (*) AC Stark effect. The interference of crossed laser beams forms an “optical” analogue of these structures, (-5[1])which in 3 dimensions come in 14 types and are built from primitive, face-centered, or body-centered unit cells. (10[1])For 10 points, (-5[1])give this term for the periodic structure formed by crystals. (10[1])■END■ (10[1])