Efimov states are an infinite series of three-body bound states that exhibit universal discrete scaling symmetry when pair-wise interactions are resonantly enhanced. Several observations of Efimov trimers have been reported in different ultracold atom experiments, however the associated scale invariance has not yet directly been observed in experiment due to the large homonuclear scaling constant λ0= 22.7. In contrast, heteronuclear systems with a large mass imbalance can possess smaller scaling constants facilitating the observation of the underlying symmetry.

In this talk I will report our investigation on the discrete scaling symmetry of Efimov states in an ultracold mixture of Li-6 and Cs-133 atoms. In this work we identified three enhanced loss features (resonances) associated with three trimer states near an interspecies Feshbach resonance. From the positions of the three resonances, we determine a geometric scaling factor of 4.9(4), in good agreement with the theoretical prediction. Our result represents a model-independent experimental demonstration of discrete scaling symmetry in three-body systems.

Reference: 

S.-K. Tung et al., Geometric Scaling of Efimov States in a Li−Cs Mixture, Phys. Rev. Lett. 113, 240402 (2014)