The microscopic laws of quantum mechanics can influence behavior at the macroscopic scale. In superconductors, for example, the coupling of electrons into Cooper pairs leads to current flow without resistance. In superfluids, the collective motion of atoms as a coherent matter wave suppresses dissipation and produces frictionless mass flow. Both phenomena starkly contrast with our everyday experience. Recent experiments with ultracold gases of magnetic atoms have demonstrated that a long sought after and, perhaps, even more counterintuitive “super” state exists: the supersolid, a state that combines the properties of a solid and a superfluid.
One of the fundamental principles of quantum mechanics is the superposition principle. A single atom can be not only in a particular quantum state, such as spin up or down, but also in a coherent superposition of two such states.
Since the 1950s theoretical physicists have pondered whether quantum mechanics allows for a phase of matter—that...
