We report a detailed molecular spectroscopy study on the lowest excited electronic states of $^{ 23}\rm{ Na}^{ 87}\rm{ Rb}$ for producing ultracold $^{ 23}\rm{ Na}^{ 87}\rm{ Rb}$ molecules in the electronic, rovibrational and hyperfine ground state. Starting from weakly-bound Feshbach molecules, a series of vibrational levels of the $A^{ 1}\Sigma^{ +}-b^{ 3}\Pi$ coupled excited states were investigated. After resolving, modeling and interpreting the hyperfine structure of several lines, we successfully identified a long-lived level resulting from the accidental hyperfine coupling between the $0^+$ and $0^-$ components of the $b^3\Pi$ state, satisfying all the requirements for the population transfer toward the lowest rovibrational level of the X$^1\Sigma^+$ state. Using two-photon spectroscopy, its binding energy was measured to be 4977.308(3) cm$^{ -1}$, the most precise value to date. We calibrated all the transition strengths carefully and also demonstrated Raman transfer of Feshbach molecules to the absolute ground state.
Categories: cond-mat.quant-gas physics.atom-ph