Optical cooling and trapping of highly magnetic atoms: the benefits of a spontaneous spin polarization

Abstract

From the study of long-range-interacting systems to the simulation of gauge fields, open-shell Lanthanide atoms with their large magnetic moment and narrow optical transitions open novel directions in the field of ultracold quantum gases. As for other atomic species, the magneto-optical trap (MOT) is the working horse of experiments but its operation is challenging, due to the large electronic spin of the atoms. Here we present an experimental study of narrow-line Dysprosium MOTs. We show that the combination of radiation pressure and gravitational forces leads to a spontaneous polarization of the electronic spin. The spin composition is measured using a Stern-Gerlach separation of spin levels, revealing that the gas becomes almost fully spinpolarized for large laser frequency detunings. In this regime, we reach the optimal operation of the MOT, with samples of typically 3 × 10 8 atoms at a temperature of 15 µK. The spin polarization reduces the complexity of the radiative cooling description, which allows for a simple model accounting for our measurements. We also measure the rate of density-dependent atom losses, finding good agreement with a model based on light-induced Van der Waals forces. A minimal two-body loss rate β ∼ 2 × 10 −11 cm 3 /s is reached in the spin-polarized regime. Our results constitute a benchmark for the experimental study of ultracold gases of magnetic Lanthanide atoms. arXiv:1610.02284v2 [cond-mat.quant-gas]

Production of a degenerate Fermi-Fermi mixture of dysprosium and potassium atoms

“…Magneto-optical traps Our dysprosium preparation scheme is similar to the one described in Refs. [73,74]. As a source of Dy atoms, we use a high-temperature effusion oven operating at about 1000 • C combined with a Zeeman slower operating on the broad line (natural linewidth of 32 MHz) at 421 nm.…”

Anisotropic optical trapping as a manifestation of the complex electronic structure of ultracold lanthanide atoms: The example of holmium

“…Therefore the sum in Eq. (27) runs over the quantum numbersJ,J v andL v . If we express the squared reduced transition dipole moment as in Eq.…”

“…(27) with |βJ = |0J . Assuming that the transition is due to the coupling between the basis states |1J ′′ and |0J , we obtain that the squared transition dipole moment is proportional to w…”

“…In particular, the squares of the transition dipole moments are extracted from Einstein coefficients, by reversing Eq. (27),…”

“…In fact, the interest for ultracold lanthanide atoms is motivated by several topics in current research, including ultracold collisions and quantum chaos [1][2][3], dipolar quantum gases with large magnetic moment and strong dipole-dipole interaction [4][5][6][7][8], many-body quantum systems [9,10], exotic quantum phases [11][12][13] like stable quantum droplets [14][15][16], synthetic gauge field [17,18], and optical clocks [19][20][21]. Recent progress in laser cooling and magnetooptical trapping of high-atomic-number (high-Z) lanthanides [22,23], including dysprosium (Dy) [24][25][26][27], erbium (Er) [28][29][30], holmium (Ho) [31] and thulium (Tm) [32] is paving the way towards these investigations. In addition, both Bose-Einstein condensates and quantumdegenerate Fermi gases have been produced in isotopes of Dy [4,33,34] and Er [35,36].…”