Figure 1

Bose polaron properties at the Feshbach resonance. (a) shows the theoretical values of the interspecies scattering length \(a_{\mathrm {IB}}\) and the three-body loss coefficient \(K_{3}\) for Rb-Rb-Cs scattering at the 181 G Feshbach resonance (dashed red). For our typical BEC density of 10¹⁴ cm⁻³ the estimated coupling strength α and the corresponding polaron energy \(E_{\mathrm{p}}\) is shown in (b). The vertical blue shaded area indicates fulfillment of the condition \(\beta= \nu_{\mathrm{p}}/\gamma_{\mathrm{p}} > 5\) (>1 light shaded). (c) The parameter ϵ is derived in [7] and gives an estimate of how well the Bose polaron fits the Fröhlich type. The horizontal green shaded area indicates \(\epsilon<0.3\) which means good correspondence to the Fröhlich type polaron.