  This paper investigates point-to-point information transmission over a
wideband slow-fading channel, modeled as an (asymptotically) large number of
independent identically distributed parallel channels, with the random channel
fading realizations remaining constant over the entire coding block. On the one
hand, in the wideband limit the minimum achievable energy per nat required for
reliable transmission, as a random variable, converges in probability to
certain deterministic quantity. On the other hand, the exponential decay rate
of the outage probability, termed as the wideband outage exponent,
characterizes how the number of parallel channels, {\it i.e.}, the
``bandwidth'', should asymptotically scale in order to achieve a targeted
outage probability at a targeted energy per nat. We examine two scenarios: when
the transmitter has no channel state information and adopts uniform transmit
power allocation among parallel channels; and when the transmitter is endowed
with an one-bit channel state feedback for each parallel channel and
accordingly allocates its transmit power. For both scenarios, we evaluate the
wideband minimum energy per nat and the wideband outage exponent, and discuss
their implication for system performance.
