Traditional 1D bar codes (with printed bars and spaces) are giving way to 2D bar codes that also include dots, hexagons, and even colors to encode more data. Bar-code scanners read 1D bar codes.

Figure 1: Unlocking of the 2D vortex lattice on a linear potential. In Fig. 2a we show a sequence of vortex lattice images between 0.5 T and 5.5 T. We identify three different phases. In phase I ...