Temperature dependence of an Efimov resonance in K39

Abstract

Ultracold atomic gases are an important testing ground for understanding few-body physics. In particular, these systems enable a detailed study of the Efimov effect. We use ultracold 39 K to investigate the temperature dependence of an Efimov resonance. The shape and position of the observed resonance are analyzed by employing an empirical fit, and universal finite-temperature zero-range theory. Both procedures suggest that the resonance position shifts towards lower absolute scattering lengths when approaching the zero-temperature limit. We extrapolate this shift to obtain an estimate of the three-body parameter at zero temperature. A surprising finding of our study is that the resonance becomes less prominent at lower temperatures, which currently lacks a theoretical description and implies physical effects beyond available models. Finally, we present measurements performed near the Feshbach resonance center and discuss the prospects for observing the second Efimov resonance in 39 K. arXiv:1807.05001v2 [cond-mat.quant-gas]

Precision Test of the Limits to Universality in Few-Body Physics

“…4), where na 3 = 9.7 × 10 −5 at a − . A recently published study [30], on the same resonance as we discuss here, reports difficult-to-interpret results, including counter-intuitive temperature-induced shifts in the Efimov peak at high values of na 3 and nλ 3 . We see no such effects in the data (shown in Fig.…”

“…In this Letter, we present a precise test of the van arXiv:1907.00729v1 [cond-mat.quant-gas] 1 Jul 2019 [13]. Previous results (blue circles) [3,15,[18][19][20][21][22][23][24][25][26][27][28][29][30] show a tentative dependence of a− value on the Feshbach resonance strength parameter sres. Our measurement (red star; red band in the inset) is the strongest evidence of departure from the −9.7±15% r vdW value (dashed line and gray area) predicted by van der Waals universality [4,5,7,8].…”

“…One might expect the threebody Efimov resonances to be more precisely universal when they fall more deeply within the range of a for which the two-body Feshbach resonant structure is universal. In previous experiments on homonuclear Efimov states [3,15,[18][19][20][21][22][23][24][25][26][27][28][29][30] there is some support for the notion that as s res gets smaller, the measured a − values should begin to deviate from the universal a − = −9.7 r vdW value, see Fig. 1.…”

“…1. However, this conclusion is only tentative due to: large experimental uncertainties in the measured a − [15]; mysterious temperature dependence [30]; the use of indirect methods in measuring a − [13]; and large systematic uncertainties in the parameters of the underlying twobody Feshbach resonance [15,18,19,25].…”