  We show that with adiabatic passage, one can reliably drive two-photon
optical transitions between the ground states and interacting Rydberg states in
a pair of atoms. For finite Rydberg interaction strengths a new adiabatic
pathway towards the doubly Rydberg excited state is identified when a constant
detuning is applied with respect to an intermediate optically excited level.
The Rydberg interaction among the excited atoms provides a phase that may be
used to implement quantum gate operations on atomic ground state qubits.
