Crossing a Quantum Fluid Divide

Understanding superfluidity and superconductivity in two dimensions (2D) has long challenged and intrigued physicists. In the early 1990s, 2D quantum fluids provided a preliminary model for the motion of electrons in layered high-temperature superconductors. Since then, alternative theories have been put forth, but there is growing interest in understanding how confinement to two dimensions can influence the flow of quantum particles. An exciting arena for studying 2D quantum fluids is atomic physics, where ultracold atoms have the advantage that their interactions can be fairly easily manipulated with electromagnetic fields. Writing in Physical Review Letters, Vasiliy Makhalov and colleagues from the Russian Academy of Sciences in Nizhniy Novgorod report measurements of the ground-state pressure of a 2D cloud of atoms as the binding between the atoms is increased. By monitoring the gas pressure, they were able to observe how pairs of these fermionic atoms transform into tightly bound bosonic molecules [1]. The properties of this fermion-to-boson crossover will help refine theories of strongly correlated quantum fluids in 2D.