Quantum State Singlet-Triplet Character Control in 7Li2

Abstract

We have demonstrated a means of quantum control by all-optical control of valence electron spin polarization in the lithium dimer. The energy levels of interest are two closely spaced rovibrational levels (the G1Πg (12, 21f) and 13Sg- (1, 21f) states separated by 720 MHz). In the absence of any optical fields, the spin-orbit interaction couples the two states, resulting in each state being a mixture of the pure singlet and pure triplet states. The initial mixing coefficients are governed by the strength of the spin-orbit coupling between the two levels. In lithium dimer, this mixing is very weak; the nominal singlet (triplet) state is initially 87% singlet (triplet) and 13% triplet (singlet). When a strong coupling field is applied to the nominally singlet state, an Autler-Townes (AT) split pair is created. Since one of the AT components is pushed closer in energy to the nearby triplet state, the triplet state gains more singlet character. Since the AT splitting is dependent upon the magnitude of the applied coupling field Rabi frequency, the mixing coefficients of the perturbed pair can therefore be coherently controlled. Such control may be useful for applications in cold molecule formation and control of predissociation rates, and may also provide insight into the role that valence electron spin polarization plays in reactive collisions.