  It is a fundamental principle of quantum theory that an unknown state cannot
be copied or, as a consequence, an unknown optical signal cannot be amplified
deterministically and perfectly. Here we describe a protocol that provides
nondeterministic quantum optical amplification in the coherent state basis with
high gain, high fidelity and which does not use quantum resources. The scheme
is based on two mature quantum optical technologies, coherent state comparison
and photon subtraction. The method compares favourably with all previous
nondeterministic amplifiers in terms of fidelity and success probability.
