We explore possible pathways for the creation of ultracold polar NaK molecules in their absolute electronic and rovibrational ground state starting from ultracold Feshbach molecules. In particular, we present a multi-channel analysis of the electronic ground and K(4p)+Na(3s) excited state manifold of NaK, analyze the spin character of both the Feshbach molecular state and the electronically excited intermediate states and discuss possible coherent two-photon transfer paths from Feshbach molecules to rovibronic ground state molecules. The theoretical study is complemented by the demonstration of STIRAP transfer from the X 1 Σ + (v=0) state to the a 3 Σ + manifold on a molecular beam experiment.

We provide spectroscopic data for the a 3E+ state of the 23Na39K molecule. The experiment is done in an ultrasonic beam apparatus, starting from the ground state X 'E + and driving the population to the a 3S + state, using a A scheme with fixed pump and scanning dump laser. The signals are observed as dips of the total fluorescence. The intermediate level is chosen to be strongly perturbed by the B 1 n / c 3E + states mixing to overcome the singlet-triplet transfer prohibition. We observed highly resolved hyperfine spectra of various rovibrational levels of the a 3E + state from va = 2 up to the highest vibrational levels for rotational quantum numbers Na = 4,6,8. By the typical experimental linewidth of 17 MHz, the vibrational dependence of the hyperfine splitting is clearly revealed for NaK. The absolute frequency measurements of the vibrational levels are used for improvement of the a 'E + potential curve and of the derived scattering length of all natural isotope combinations. Applying the A scheme in the reverse direction can provide a pathway for efficient transfer of ultracold 23Na39K molecules from the Na(3s) 4-K(4s) asymptote to the lowest levels of the ground state. We show spectra that couple the absolute ground state Vx = 0. J = 0 with an appropriate intermediate state for direct realization of the reverse path. The refined theoretical model of the coupled excited states of the Na(3s) + K(4p) asymptote allows predictions of efficient paths for 23Na4(,K; one example is calculated.

No abstract