# Random to chaotic temperature transition in low-field Fano-Feshbach resonances of cold thulium atoms

## TL;DR

This study observes a transition from random to chaotic resonance spacing in ultracold thulium atoms, revealing new resonance behaviors and providing insights into their scattering properties relevant for Bose-Einstein Condensation.

## Contribution

It reports the first observation of a temperature-induced transition in Fano-Feshbach resonance statistics and determines the background scattering length of thulium.

## Key findings

- Transition from random to chaotic resonance spacing with temperature
- Different temperature shifts for s- and d-resonances
- Estimated background scattering length of thulium as 144±38 a.u.

## Abstract

Here, we report on the observation of a random to chaotic temperature transition in the spacing of Fano-Feshbach resonances in the ultracold polarized gas of thulium atoms. This transition is due to the appearance of so-called d-resonances, which are not accessible at low temperatures, in the spectra at high temperatures, which drastically changes thulium's overall resonance statistic. In addition to this statistical change, it has been observed that s- and d-resonances experience quite different temperature shifts: s-resonances experience almost no shift with the temperature, while d-resonances experience an obvious positive shift. In addition, careful analysis of the broad Fano-Feshbach resonances enabled the determination of the sign of thulium's background scattering length. A rethermalization experiment made it possible to estimate a length value of a=144+-38a.u.. This proves that thulium atoms are suitable for achieving Bose-Einstein Condensation.

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Source: https://tomesphere.com/paper/1902.00201