Dear Editor,

please find enclosed our manuscript entitled "Reversing the temporal envelope
of a heralded single photon using a cavity". Building on a narrowband heralded
photon source based on four-wave mixing in a cold atomic vapor, we manage to
manipulate the biphoton wavefunction emerging from a cascade decay in Rubidium
atoms with a cavity in one of the modes in a way that results in a heralded
photon with a rising exponential envelope that is resonant with an atom in the
ground state.

While our work is mostly experimental, we present a relatively simple model to
describe the transformation the cavity induces in the biphoton system, and
verify its predictive power not only for the preparation of heralded photons
with a rising exponential shape, but also for a more complex situation.

We believe that this work is a significant advancement in the preparation of
photons of that envelope, and a necessary component in a quantum information
processing system where information has to be transferred from photons back to
atoms. It should be interesting to a wider physics community as well, as the
technique illustrates that phase shifting on one part of a biphoton can affect
the temporal shape of the other photon of this pair - a transformation that is
not immediately obvious.

We therefore feel that Physical Review Letters should be an adequate platform
for this work, and look forward to your reply.

With Best Regards on behalf of all authors,

Christian Kurtsiefer