  Inherent loss is always to be avoided in generating single photons or
biphotons, but interestingly it provides opportunities for manipulating the
photon wave packet. In this paper we show how inherent loss in parametric
down-conversion can be employed to tailor the wave packets of single photons
and biphotons. As an example, we propose a scheme to realize a single photon in
a single cycle using inherent loss. Our work has potential applications in
quantum communication, quantum computation, and quantum interface.
