Phase transitions in artificial atoms

Modern techniques of lithography make it possible to confine electrons to sufficiently small dimensions that the quantization of their energy and charge is easily observable. Whereas the artificial atoms so formed behave in many ways Like natural ones, new physics is observed because their level spacing is smaller than that of natural atoms. In particular, a phase transition as a function of magnetic field between the spin singlet state and the spin polarized state has recently been observed in artificial atoms that is inaccessible at reasonable magnetic fields in natural atoms. We present a simple explanation of the physics of this transition.