Emergence of chaotic scattering in ultracold Er and Dy

• Published in: arXiv.org 2015-10
• Main Authors: Maier, T, Kadau, H, Schmitt, M, Wenzel, M, Ferrier-Barbut, I, Pfau, T, Frisch, A, Baier, S, Aikawa, K, Chomaz, L, Mark, M J, Ferlaino, F, Makrides, C, Tiesinga, E, Petrov, A, Kotochigova, S
• Format: Article
• Language: English
• Subjects: Anisotropy; Computer simulation; Coupling (molecular); Dependence; Dysprosium; Erbium; Magnetic fields; Magnetic properties; Magnetic resonance; Scattering
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1506.05221

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.