  We have used deterministic single-photon two qubit (SPTQ) quantum logic to
implement the most powerful individual-photon attack against the
Bennett-Brassard 1984 (BB84) quantum key distribution protocol. Our measurement
results, including physical source and gate errors, are in good agreement with
theoretical predictions for the Renyi information obtained by Eve as a function
of the errors she imparts to Alice and Bob's sifted key bits. The current
experiment is a physical simulation of a true attack, because Eve has access to
Bob's physical receiver module. This experiment illustrates the utility of an
efficient deterministic quantum logic for performing realistic physical
simulations of quantum information processing functions.
