Emergence of chaotic scattering in ultracold Er and Dy

TL;DR

This study demonstrates the emergence of chaotic scattering in ultracold Er and Dy atoms caused by anisotropic interactions and magnetic fields, combining experimental measurements with theoretical models to analyze Feshbach resonances and their statistical properties.

Contribution

The paper provides the first combined experimental and theoretical analysis of chaotic scattering in ultracold lanthanide atoms, revealing the role of anisotropic interactions and Zeeman coupling in Feshbach resonance spectra.

Findings

Chaotic scattering emerges due to anisotropic interactions and magnetic fields.

Feshbach resonance spectra exhibit statistical properties consistent with random matrix theory.

Resonant non-zero partial-wave collisions cause extreme temperature sensitivity in atom-loss spectra.

Abstract

We show that for ultracold magnetic lanthanide atoms chaotic scattering emerges due to a combination of anisotropic interaction potentials and Zeeman coupling under an external magnetic field. This scattering is studied in a collaborative experimental and theoretical effort for both dysprosium and erbium. We present extensive atom-loss measurements of their dense magnetic Feshbach resonance spectra, analyze their statistical properties, and compare to predictions from a random-matrix-theory inspired model. Furthermore, theoretical coupled-channels simulations of the anisotropic molecular Hamiltonian at zero magnetic field show that weakly-bound, near threshold diatomic levels form overlapping, uncoupled chaotic series that when combined are randomly distributed. The Zeeman interaction shifts and couples these levels, leading to a Feshbach spectrum of zero-energy bound states with nearest-neighbor spacings that changes from randomly to chaotically distributed for increasing magnetic field. Finally, we show that the extreme temperature sensitivity of a small, but sizeable fraction of the resonances in the Dy and Er atom-loss spectra is due to resonant non-zero partial-wave collisions. Our threshold analysis for these resonances indicates a large collision-energy dependence of the three-body recombination rate.