All-optical control of pendular qubit states with nonresonant two-color laser pulses

Practical methodologies for qubit controls are established by two prerequisites, i.e., preparation of a well-defined initial quantum state and coherent control of that quantum state. Here we propose a quantum control method, realized by irradiating nonresonant nanosecond two-color (omega and 2 omega) laser pulses to molecules in the pendular (field-dressed) ground state. The two-color field nonadiabatically splits the initial pendular ground state vertical bar(0) over tilde,(0) over tilde > to a superposition state of vertical bar(0) over tilde,(0) over tilde > and vertical bar(1) over tilde,(0) over tilde >, whose relative probability amplitudes can be controlled by the peak intensity of one wavelength component (omega) while the peak intensity of the other component (2 omega) is fixed. The splitting of the quantum paths is evidenced by observing degrees of orientation of ground-state-selected OCS molecules by the velocity map imaging technique. This quantum control method is highly advantageous because any polar molecule can be controlled regardless of the molecular energy structures.