Magnetic trapping of rare-earth atoms at millikelvin temperatures

The ability to create quantum degenerate gases has led to the realization of Bose–Einstein condensation of molecules1,2,3,4, atom–atom entanglement5 and the accurate measurement of the Casimir force in atom–surface interactions6. With a few exceptions7,8,9, the achievement of quantum degeneracy relies on evaporative cooling of magnetically trapped atoms to ultracold temperatures. Magnetic traps confine atoms whose electronic magnetic moments are aligned anti-parallel to the magnetic field. This alignment must be preserved during the collisional thermalization of the atomic cloud. Quantum degeneracy has been reached in spherically symmetric, S-state atoms (atoms with zero internal orbital angular momentum). However, collisional relaxation of the atomic magnetic moments of non-S-state atoms (non-spherical atoms with non-zero internal orbital angular momentum) is thought to proceed rapidly. Here we demonstrate magnetic trapping of non-S-state rare-earth atoms, observing a suppression of the interaction anisotropy in collisions. The atoms behave effectively like S-state atoms because their unpaired electrons are shielded by two outer filled electronic shells that are spherically symmetric. Our results are promising for the creation of quantum degenerate gases with non-S-state atoms, and may facilitate the search for time variation of fundamental constants10,11,12 and the development of a quantum computer with highly magnetic atoms13.