  I study the evolution of mean field and linear quantum fluctuations in a
toroidal Bose-Einstein condensate, whose interaction strength is quenched from
a finite (repulsive) value to zero. The azimuthal equal-time density-density
correlation function is calculated and shows temporal oscillations with twice
the (final) excitation frequencies after the transition. These oscillations are
a direct consequence of positive and negative frequency mixing during
non-adiabatic evolution. I will argue that a time-resolved measurement of the
equal-time density correlator might be used to calculate the moduli of the
Bogoliubov coefficients and thus the amount of squeezing imposed on a mode,
i.e., the number of atoms excited out of the condensate.

Quantum Gases