  Sakharov oscillations, conventionally discussed in the context of early
universe evolution and the anisotropy of cosmic microwave background radiation,
is the manifestation of interfering acoustic waves synchronously generated in
an ideal fluid. Here we report the laboratory demonstration of Sakharov
oscillations in a quenched atomic superfluid. We quench the sample by Feshbach
tuning and monitor the subsequent density fluctuations at different time and
length scales by in situ imaging. Sakharov oscillations are identified as the
multi-peak structure in the atomic density power spectrum, resembling that of
the cosmic microwave background. We also observe Sakharov oscillations in the
time domain, from which we extract the energy dispersion of the superfluid, and
determine the sonic horizon of the excitations.

Quantum Gases;Cosmology and Nongalactic Astrophysics