The four-level exciton/biexciton system of a single semiconductor quantum dot
acts as a two qubit register. We experimentally demonstrate an
exciton-biexciton Rabi rotation conditional on the initial exciton spin in a
single InGaAs/GaAs dot. This forms the basis of an optically gated two-qubit
controlled-rotation (CROT) quantum logic operation where an arbitrary exciton
spin is selected as the target qubit using the polarization of the control
laser.Comment: 4- pages, 4 figures, to be submitted to PR