  Quantum fluctuations are the origin of genuine quantum many-body effects, and
can be neglected in classical mean-field phenomena. Here we report on the
observation of stable quantum droplets containing $\sim$ 800 atoms which are
expected to collapse at the mean-field level due to the essentially attractive
interaction. By systematic measurements on individual droplets we demonstrate
quantitatively that quantum fluctuations stabilize them against the mean-field
collapse. We observe in addition interference of several droplets indicating
that this stable many-body state is phase coherent.
