We propose a mechanism to produce a superposition of atomic and molecular states by a train of ultrashort laser pulses combined with weak control fields. By adjusting the repetition rate of the pump pulses and the intensity of the coupling laser, one can suppress a transition while simultaneously enhancing the desired transitions. As an example, various superpositions of vibrational states of the ${\mathrm{K}}_2$ molecule are shown.

• Received 30 November 2009

DOI:https://doi.org/10.1103/PhysRevA.81.033401