  The capacity of a quantum channel for transmission of classical information
depends in principle on whether product states or entangled states are used at
the input, and whether product or entangled measurements are used at the
output. We show that when product measurements are used, the capacity of the
channel is achieved with product input states, so that entangled inputs do not
increase capacity. We show that this result continues to hold if sequential
measurements are allowed, whereby the choice of successive measurements may
depend on the results of previous measurements.
  We also present a new simplified expression which gives an upper bound for
the Shannon capacity of a channel, and which bears a striking resemblance to
the well-known Holevo bound.
