Narrow-line magneto-optical trap for europium

We report on the realization of a magneto-optical trap (MOT) for europium atoms using a narrow-line cooling transition with a natural linewidth of 97 kHz. Europium is a strongly dipolar species with interesting properties, such as the presence of hyperfine structure and the absence of electronic orbital angular momentum. Our starting point of the MOT is continuous capturing and cooling of optically pumped metastable europium atoms. We have employed simultaneous MOT for the metastable and ground-state atoms. The trapped metastable atoms are successively pumped back to the ground state and then continuously loaded to the narrow-line MOT, where up to 4.7 ×10⁷ atoms are captured. A spin-polarized sample at a temperature of 6 μ K and with a peak number density of 2.2 ×10¹¹cm⁻³ is obtained through the compression process, resulting in a phase space density of 3 ×10⁻⁵ .