Arbitrary state controlled-unitary gate by adiabatic passage

Abstract

We propose a fast scheme involving atoms fixed in an optical cavity to directly implement the universal controlled-unitary gate. The present technique based on adiabatic passage uses dark states well suited for the controlled-rotation operation. We show that these dark states allow the robust implementation of a gate that is a generalization of the controlled-unitary gate to the case where the control qubit can be selected to be an arbitrary state. This gate has potential applications to the rapid implementation of quantum algorithms such as the projective measurement algorithm. This process is decoherence-free since excited atomic states and cavity modes are not populated during the dynamics.