  We demonstrate the simultaneous propagation of slow- and fast-light optical
pulses in a four-wave mixing scheme using warm potassium vapor. We show that
when the system is tuned such that the input probe pulses exhibit slow-light
group velocities and the generated pulses propagate with negative group
velocities, the information velocity in the medium is nonetheless constrained
to propagate at, or less than, c. These results demonstrate that the transfer
and copying of information on optical pulses to those with negative group
velocities obeys information causality, in a manner that is reminiscent of a
classical version of the no-cloning theorem. Additionally, these results
support the fundamental concept that points of non-analyticity on optical
pulses correspond to carriers of new information.
