Dynamics and Thermodynamics of the Low-Temperature Strongly Interacting Bose Gas

We measure the zero-temperature equation of state of a homogeneous Bose gas of Li-7 atoms by analyzing the in situ density distributions of trapped samples. For increasing repulsive interactions our data show a clear departure from mean-field theory and provide a quantitative test of the many-body corrections first predicted in 1957 by Lee, Huang, and Yang [Phys. Rev. 106, 1135 (1957).]. We further probe the dynamic response of the Bose gas to a varying interaction strength and compare it to simple theoretical models. We deduce a lower bound for the value of the universal constant xi > 0.44(8) that would characterize the universal Bose gas at the unitary limit.