  We consider the unambiguous discrimination between two unknown qudit states
in $n$-dimensional ($n\geqslant2$) Hilbert space. By equivalence of unknown
pure states to known mixed states and with the Jordan-basis method, we
demonstrate that the optimal success probability of the discrimination between
two unknown states is independent of the dimension $n$. We also give a scheme
for a physical implementation of the programmable state discriminator that
unambiguously discriminate between two unknown states with optimal probability
of success.
