  The notion of many-body quantum scars is associated with special eigenstates,
usually concentrated in certain parts of Hilbert space, that give rise to
robust persistent oscillations in a regime that globally exhibits
thermalization. Here we extend these studies to many-body systems possessing a
true classical limit characterized by a high-dimensional chaotic phase space,
which are not subject to any particular dynamical constraint. We demonstrate
genuine quantum scarring of wave functions concentrated in the vicinity of
unstable classical periodic mean-field modes in the paradigmatic Bose-Hubbard
model. These peculiar quantum many-body states exhibit distinct phase-space
localization about those classical modes. Their existence is consistent with
Heller's scar criterion and appears to persist in the thermodynamic
long-lattice limit. Launching quantum wave packets along such scars leads to
observable long-lasting oscillations, featuring periods that scale
asymptotically with classical Lyapunov exponents, and displaying intrinsic
irregularities that reflect the underlying chaotic dynamics, as opposed to
regular tunnel oscillations.
