  We propose an extension of coherent control using laser-synthesized
free-electron matter waves. In contrast to coherent control schemes exploiting
optical coherences to steer the dynamics of matter waves, we analyze the
opposite and investigate the control of quantum light emission driven by
laser-sculpted coherent free-electron matter waves. We apply this concept to
the control of entangled photon-pair emission in electron-atom collisions, in
which the incident electron wave packet, colliding with a target atom $B$, is
engineered by interferometric resonantly-enhanced multiphoton ionization of a
parent atom $A$. Each ionization pathway leads to electron wave packets that
coherently interfere during temporal evolution in the continuum. Their mutual
coherence can be controlled by adjusting the relative phases or time delays of
the frequency components of the ionizing field contributing to the interfering
pathways. We report coherent control of entangled photon-pair generation in
radiative photo-cascade emission upon decay of the target atom after inelastic
excitation triggered by the collision with the synthesized electron wave
packet.
