Phys. Rev. X 4, 021011 (2014)

Credit: © ISTOCKPHOTO.COM / PESKYMONKEY.

Well-isolated and pure, quantum gases offer a promising test bed for investigating how closed quantum systems relax to equilibrium — a fundamental problem in many-body physics. The effect of spin on the relaxation of bosonic quantum gases has previously been explored, but Ulrich Ebling and colleagues now elucidate the relaxation processes when Pauling blocking is added to the mix.

Starting with just two of the ten available spin states occupied, Ebling et al. observed the relaxation of a large-spin fermionic gas of potassium atoms. With spin and spatial degrees of freedom both involved, complex dynamics drive a redistribution among all spin states. Indeed, several different collision processes that cause spin changes, occurring on different timescales, were observed by the authors.

Although collision-assisted spin redistribution was the slowest process in the system, changes in the gas density could alter the relaxation rate by orders of magnitude. Ebling et al. also showed that the relaxation dynamics could be further controlled by tuning an applied magnetic field.