Collapse and revival of the monopole mode of a Bose-Einstein condensate in a spherical harmonic trap

We observe the relaxation of the monopole (breathing) mode of a rubidium-87 Bose-Einstein condensate (BEC) in a highly spherical harmonic trap [1] at finite temperature. The experiments show a collapse and revival of the condensate oscillation, consistent with numerical simulations of the system using the Zaremba-Nikuni-Griffin methodology for the nonequilibrium dynamics of BECs [2]. The beating signal is shown to be due to the resonant excitation of the ``out-of-phase'' normal mode of the condensate and thermal cloud. [1] D. S. Lobser, A. E. S. Barentine, E. A. Cornell, and H. J. Lewandowski, Nat. Phys. 11, 1009 (2015). [2] E. Zaremba, T. Nikuni, and A. Griffin, J. Low Temp. Phys. 116, 277 (1999).