BEC Collapse and Dynamical Squeezing of Vacuum Fluctuations

(May 18, 2003, second version of cond-mat/0207289 deposited in arXiv on July 11, 2002. umdpp02-61)AbstractWe analyzethe phenomena ofcondensatecollapse, asdescribed byDonley et al [1, 2], by focusingon the behavior of excitations or fluctuations above the condensate, as driven by the dynamics ofthe condensate, rather than the dynamics of the condensate alone or the kinetics of the atoms. Thedynamics of the condensate squeezes and amplifies the quantum excitations, mixing the positiveand negative frequency components of their wave functions thereby creating particles which appearas bursts and jets. By analyzing the changing amplitude and particle content of these excitations,our simple physical picture explains well the overall features of the collapse phenomena and provideexcellent quantitative fits with experimental data on several aspects, such as the scaling behavior ofthe collapse time and the amount of particles in the jet. The predictions of the bursts at this levelof approximation is less than satisfactory but may be improved on by including the backreactionof the excitations on the condensate. The mechanism behind the dominant effect – parametricamplification of vacuum fluctuations and freezing of modes outside of horizon – is similar to that ofcosmological particle creation and structure formation in a rapid quench (which is fundamentallydifferent from Hawking radiation in black holes). This shows that BEC dynamics is a promisingvenue for doing ‘laboratory cosmology’.