Testing universality of Efimov physics across broad and narrow Feshbach resonances

Efimov physics is a universal phenomenon in quantum three-body systems. For systems with resonant two-body interactions, Efimov predicted an infinite series of three-body bound states with geometric scaling symmetry(1). These Efimov states, first observed in cold caesium atoms(2), have been recently reported in a variety of other atomic systems(3-13). The intriguing prospect of a universal absolute Efimov resonance position across Feshbach resonances remains an open question. Theories predict a strong dependence on the resonance strength for closed-channel-dominated Feshbach resonances, whereas experimental results have so far been consistent with the universal prediction. Here we directly compare the Efimov spectra in a Li-6-Cs-133 mixture near two Feshbach resonances which are very different in their resonance strengths, but otherwise almost identical. Our result shows a clear dependence of the absolute Efimov resonance position on Feshbach resonance strength and a clear departure from the universal prediction for the narrow Feshbach resonance.