Thanks to teams at two laboratories, that textbook abstraction of quantum mechanics, the one‐dimensional square well, has become realized in a physical object. Known as a “heterostructure,” this object consists of accurately deposited thin layers of two different semiconductors of matching lattice constants. When these man‐made square wells are built up into stacks of 10–100 periods, they constitute essentially an infinite configuration (because of the finite mean free path of the carriers) known as a “superlattice” (PHYSICS TODAY, August 1973, page 20). These structures open the possibility of creating quantum states with predetermined energy levels and bandwidths.