  Upper bounds are given for the weight distribution of binary weakly self-dual
codes. To get these new bounds, we introduce a novel method of utilizing
unitary operations on Hilbert spaces. This method is motivated by recent
progress on quantum computing. This new approach leads to much simpler proofs
for such genre of bounds on the weight distributions of certain classes of
codes. Moreover, in some cases, our bounds are improvements on the earlier
bounds. These improvements are achieved, either by extending the range of the
weights over which the bounds apply, or by extending the class of codes
subjected to these bounds.
