Anisotropic light-shift and magic-polarization of the intercombination line of Dysprosium atoms in a far-detuned dipole trap

TL;DR

This study investigates the anisotropic light-shift and identifies a magic polarization in Dysprosium atoms within a far-detuned dipole trap, enabling optimized cooling and Bose-Einstein condensate production.

Contribution

It provides the first measurement of scalar and tensorial polarizability components for Dy's intercombination line and introduces a theoretical model predicting these values.

Findings

Identified a magic polarization where ground and excited state polarizabilities are equal.

Measured scalar and tensor polarizability components for the Dy intercombination line.

Achieved Bose-Einstein condensation of $^{162}$Dy with 30,000 atoms.

Abstract

We characterize the anisotropic differential ac-Stark shift for the Dy $626$ nm intercombination transition, induced in a far-detuned $1070$ nm optical dipole trap, and observe the existence of a "magic polarization" for which the polarizabilities of the ground and excited states are equal. From our measurements we extract both the scalar and tensorial components of the dynamic dipole polarizability for the excited state, $\alpha_E^\text{s} = 188 (12)\,\alpha_\text{0}$ and $\alpha_E^\text{t} = 34 (12)\,\alpha_\text{0}$, respectively, where $\alpha_\text{0}$ is the atomic unit for the electric polarizability. We also provide a theoretical model allowing us to predict the excited state polarizability and find qualitative agreement with our observations. Furthermore, we utilize our findings to optimize the efficiency of Doppler cooling of a trapped gas, by controlling the sign and magnitude of the inhomogeneous broadening of the optical transition. The resulting initial gain of the collisional rate allows us, after forced evaporation cooling, to produce a quasi-pure Bose-Einstein condensate of $^{162}$Dy with $3\times 10^4$ atoms.