  We study a new process, which we call ASEP$(q,j)$, where particles move
asymmetrically on a one-dimensional integer lattice with a bias determined by
$q\in (0,1)$ and where at most $2j\in\mathbb{N}$ particles per site are
allowed. The process is constructed from a $(2j+1)$-dimensional representation
of a quantum Hamiltonian with $U_q(\mathfrak{sl}_2)$ invariance by applying a
suitable ground-state transformation. After showing basic properties of the
process ASEP$(q,j)$, we prove self-duality with several self-duality functions
constructed from the symmetries of the quantum Hamiltonian. By making use of
the self-duality property we compute the first $q$-exponential moment of the
current for step initial conditions (both a shock or a rarefaction fan) as well
as when the process is started from an homogeneous product measure.
