  We investigate the out-of-equilibrium dynamics following a sudden quench of
the interaction strength, in a one-dimensional quasi-condensate trapped at the
surface of an atom chip. Within a linearized approximation, the system is
described by independent collective modes and the quench squeezes the phase
space distribution of each mode, leading to a subsequent breathing of each
quadrature. We show that the collective modes are resolved by the power
spectrum of density ripples which appear after a short time of flight. This
allows us to experimentally probe the expected breathing phenomenon. Our
results are in good agreement with theoretical predictions which take the
longitudinal harmonic confinement into account.
