Sympathetic Cooling in an Optically Trapped Mixture of Alkali and Spin-Singlet Atoms

Abstract

We report on the realization of a stable mixture of ultracold lithium and ytterbium atoms confined in a far-off-resonance optical dipole trap. We observe sympathetic cooling of 6Li by 174Yb and extract the s-wave scattering length magnitude |a(6Li-174Yb)|=(13±3)a0 from the rate of interspecies thermalization. Using forced evaporative cooling of 174Yb, we achieve reduction of the 6Li temperature to below the Fermi temperature, purely through interspecies sympathetic cooling.

Interspecies thermalization in an ultracold mixture of Cs and Yb in an optical trap

“…We expand upon the usual treatment [41,42,56,57] by including terms for evaporation [58] and single-species three-body recombination [59] as described in the Appendix. The coupled equations for the number N i and temperature T i of the two species arė…”

“…These ultracold molecules have a wealth of applications, such as tests of fundamental physics [27][28][29], realization of novel phase transitions [30][31][32], and the study of ultracold chemistry [33,34]. In addition, the long-range dipole-dipole interactions present between pairs of polar molecules make them useful in the study of dipolar quantum matter [35,36] and ultracold molecules confined in an optical lattice can simulate a variety of condensedmatter systems [37][38][39].Although the large majority of work on ultracold molecules has focused on bi-alkali systems, there is burgeoning interest in pairing alkali-metal atoms with divalent atoms such as Yb [40][41][42][43][44][45] or Sr [46]. The heteronuclear 2 Σ molecules formed in these systems have both an electric and a magnetic dipole moment in the ground electronic state.…”

“…Although the large majority of work on ultracold molecules has focused on bi-alkali systems, there is burgeoning interest in pairing alkali-metal atoms with divalent atoms such as Yb [40][41][42][43][44][45] or Sr [46]. The heteronuclear 2 Σ molecules formed in these systems have both an electric and a magnetic dipole moment in the ground electronic state.…”

Magnetically Tunable Feshbach Resonances in Ultracold Li-Yb Mixtures

“…Among the most promising candidates for this are molecules formed from an alkali-metal atom and a 1 S atom such as an alkaline earth or Yb. A number of experimental groups are studying ultracold mixtures in which such molecules might be formed, including Rb þ Yb [11] and Li þ Yb [12][13][14].…”

“…However, it is probably accurate to only a few percent, and variations within this uncertainty are enough to span the entire range of scattering length a from þ1 to À1. However, Ivanov et al [13] and Hara et al [14] have recently measured values of the scattering length to be jaj ¼ 13 AE 3a 0 (0:69 AE 0:16 nm) and 1:0 AE 0:2 nm, respectively. Because the sign of a is unknown, we have scaled the potential of Zhang et al to give two potentials, V þ and V À , with scattering lengths a ¼ þ0:8 nm and À0:8 nm, each within the error bars of both measurements.…”