Andrew Berglund, James Hanssen, Siu Au Lee, and Jabez McClelland


            The atomic structure of the rare-earth (lanthanide) elements gives rise to large magnetic moments and a variety of electronically shielded optical transitions. These magneto-optical properties are useful for many solid-state technologies, and rare-earth elements correspondingly find applications in devices such as permanent magnets, optical amplifiers, and lasers. However, their interesting magneto-optical properties are not restricted to the solid state. Here, we show that the rare-earth element erbium is a promising candidate for next-generation cold atomic physics, but conventional laser-cooling methods must be modified to account for its large magnetic moment and complex electronic structure. By balancing strong magnetic and weak optical forces in a novel magneto-optical trap, we cool a few thousand erbium atoms to the boundary of the ultracold (sub-microkelvin) temperature regime. Our experiments are promising for future investigations of diverse quantum phenomena such as nonclassical atomic motion, quantum-limited position and momentum sensors, and strongly dipolar quantum gases.