  When multiple quantum emitters radiate, their emission rate may be enhanced
or suppressed due to collective interference in a process known as super- or
subradiance. Such processes are well-known to occur also in light emission by
free charged particles. To date, all experimental and theoretical studies of
super- and subradiance in these systems involved the classical correlations
between the emitters. However, dependence on quantum correlations, such as
entanglement between different emitting particles, has not been studied. Recent
advances in coherent-shaping of free-electron wavefunctions motivate the
investigation of such quantum regimes of super- and subradiance. In this
Letter, we show how a pair of coincident path-entangled electrons can
demonstrate either super- or subradiant light emission, depending on the
two-particle wavefunction. By choosing different free-electron Bell-states, the
spectrum and emission pattern of the light can be reshaped, in a manner that
cannot be accounted for by a classical mixed state. We show these results for
light emission in any optical medium, and discuss their generalization to
many-body quantum states. Our findings suggest that light emission can be
sensitive to the explicit quantum state of the emitting matter wave, and
possibly serve as a non-destructive measurement scheme for measuring the
quantum state of many-body systems.
