Implosions as a probe for fluctuations in Bose-Einstein condensates

Quantum and thermal effects play important roles in the fluctuations of ultracold Bose gases, yet the fluctuations remain difficult to probe experimentally in 3D bulk systems. We seek to amplify these fluctuations via a quench from positive to negative scattering length. Following such a quench, initial fluctuations in the gas, whether seeded by a lattice potential, thermal fluctuations, or quantum fluctuations, are amplified on a time-scale which is fast compared to the bulk collapse of the cloud. We perform experiments on clouds seeded with an initial, well-understood density perturbation due to an optical lattice and on clouds with no externally imposed fluctuations. We compare our observations to a variety of theoretical models, which predict the static structure factor as a function of time and momentum in the collapsing gas.