Two and Three-body Contacts in the Unitary Bose Gas
  In many-body systems governed by pairwise contact interactions, a wide range of observables is linked by a single parameter, the two-body contact, which quantifies two-particle correlations. This profound insight has transformed our understanding of strongly interacting Fermi gases. Here, using Ramsey interferometry, we study coherent evolution of the resonantly interacting Bose gas, and show that it cannot be explained by only pairwise correlations. Our experiments reveal the crucial role of three-body correlations arising from Efimov physics, and provide a direct measurement of the associated three-body contact. 
Richard J. Fletcher, Raphael Lopes, Jay Man, Nir Navon, Robert P.   Smith, Martin W. Zwierlein, Zoran Hadzibabic
cond-mat.quant-gas