  We study Hawking radiation on the quantum space-time of a collapsing null
shell. We use the geometric optics approximation as in Hawking's original
papers to treat the radiation. The quantum space-time is constructed by
superposing the classical geometries associated with collapsing shells with
uncertainty in their position and mass. We show that there are departures from
thermality in the radiation even though we are not considering back reaction.
One recovers the usual profile for the Hawking radiation as a function of
frequency in the limit where the space-time is classical. However, when quantum
corrections are taken into account, the profile of the Hawking radiation as a
function of time contains information about the initial state of the collapsing
shell. More work will be needed to determine if all the information can be
recovered. The calculations show that non-trivial quantum effects can occur in
regions of low curvature when horizons are involved, as for instance advocated
in the firewall scenario.
