  Ultrafast spin dynamics on femto- to picosecond timescales is simulated
within a density-operator approach for a Co/Cu bilayer. The electronic
structure is represented in a tight-binding form; during the evolution of the
density operator, optical excitation by a femtosecond laser pulse, coupling to
a bosonic bath as well as dephasing are taken into account. Our simulations
corroborate the importance of interfaces for ultrafast transport phenomena and
demagnetisation processes. Moreover, we establish a reflow from Cu $d$ orbitals
across the interface into Co $d$ orbitals, which shows up prominently in the
mean occupation numbers. On top of this, this refilling manifests itself as a
minority-spin current proceeding several layers into the Cu region. The present
study suggests that the approach captures essential ultrafast phenomena and
provides insight into microscopic processes.
