Abstract
We investigate ultracold magnetic-field-assisted collisions in the so far unexplored ErYb system. The nonsphericity of the Er atom leads to weakly anisotropic interactions that provide the mechanism for Feshbach resonances to emerge. The resonances are moderately sparsely distributed with a density of 0.1–0.3 G−1 and exhibit chaotic statistics characterized by a Brody parameter η ≈ 0.5–0.7. The chaotic behaviour of Feshbach resonances is accompanied by strong mixing of magnetic and rotational quantum numbers in near-threshold bound states. We predict the existence of broad resonances at fields < 300 G that may be useful for the precise control of scattering properties and magnetoassociation of ErYb molecules. The high number of bosonic Er–Yb isotopic combinations gives many opportunities for mass scaling of interactions. Uniquely, two isotopic combinations have nearly identical reduced masses (differing by less than 10−5 relative) that we expect to have strikingly similar Feshbach resonance spectra, which would make it possible to experimentally measure their sensitivity to hypothetical variations of proton-to-electron mass ratio.
Highlights
One of the most important recent achievements in the field of ultracold quantum gases was the production of samples of highly magnetic atoms: chromium (Cr) [1], erbium (Er) [2] and dysprosium (Dy) [3,4,5,6]
In the chapter we describe the interaction between the erbium and ytterbium atoms focusing on details of ab initio calculations and their implications
The width, of resonances originating from higher partial waves quickly becomes vanishingly small, as the coupling of the s-wave to higher partial waves becomes weaker, and the density of states of closed channels at the threshold decreases as L quantum number increases
Summary
One of the most important recent achievements in the field of ultracold quantum gases was the production of samples of highly magnetic atoms: chromium (Cr) [1], erbium (Er) [2] and dysprosium (Dy) [3,4,5,6]. Quantum chaos emerges when the mean spacing between these bound states is comparable to the coupling strength between them In this regime the couplings cause multiple avoided crossings to emerge which results in a spaghetti-like pattern of repelling energy levels and a highly congested spectrum of overlapping resonances. The chaotic character of bound states and Feshbach resonances in ultracold collisions was found for several other systems, for example, in mixtures of Yb atoms in 1S0 and 3P2 states at large magnetic fields [28], and molecular collisions of Li atom with CaH and CaF [29].
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