Anisotropy in the Interaction of Ultracold Dysprosium

TL;DR

This paper provides a theoretical analysis of anisotropic interactions between ultracold dysprosium atoms, highlighting the significance of dispersion and magnetic dipole-dipole forces in potential exotic quantum states and spin exchange processes.

Contribution

It offers the first detailed theoretical comparison of anisotropic dispersion, magnetic dipole-dipole, and electric quadrupole interactions in ultracold dysprosium atoms, including scattering models for inelastic spin exchange.

Findings

Dispersion coefficients range between 1865 and 1890 a.u.

Electric quadrupole-quadrupole interaction is weak compared to other forces.

Spin exchange can occur at separations less than 50 a_0 with magnetic fields of 10-100 G.

Abstract

The nature of the interaction between ultracold atoms with a large orbital and spin angular momentum has attracted considerable attention. It was suggested that such interactions can lead to the realization of exotic states of highly correlated matter. Here, we report on a theoretical study of the competing anisotropic dispersion, magnetic dipole-dipole, and electric quadrupole-quadrupole forces between two dysprosium atoms. Each dysprosium atom has an orbital angular momentum L=6 and magnetic moment $\mu=10\mu_B$. We show that the dispersion coefficients of the ground state adiabatic potentials lie between 1865 a.u. and 1890 a.u., creating a non-negligible anisotropy with a spread of 25 a.u. and that the electric quadrupole-quadrupole interaction is weak compared to the other interactions. We also find that for interatomic separations $R< 50\,a_0$ both the anisotropic dispersion and magnetic dipole-dipole potential are larger than the atomic Zeeman splittings for external magnetic fields of order 10 G to 100 G. At these separations spin exchange can occur. We finish by describing two scattering models for inelastic spin exchange. A universal scattering theory is used to model loss due to the anisotropy in the dispersion and a distorted-wave-Born theory is used to model losses from the magnetic dipole-dipole interaction for the $^{164}$Dy isotope. These models find loss rates that are the same order of magnitude as the experimental value.