Efficient conversion of closed-channel-dominated Feshbach molecules of 23Na40K to their absolute ground state

We demonstrate the transfer of (NaK)-Na-23-K-40 molecules from a closed-channel-dominated Feshbach-molecule state to the absolute ground state. The Feshbach molecules are initially created from a gas of sodium and potassium atoms via adiabatic ramping over a Feshbach resonance at 78.3 G. The molecules are then transferred to the absolute ground state using stimulated Raman adiabatic passage with an intermediate state in the spin-orbit-coupled complex vertical bar c(3)Sigma(+), upsilon = 35, J = 1 > - vertical bar B-1 Pi, upsilon = 12, J = 1). Our measurements show that the pump transition dipole moment linearly increases with the closed-channel fraction. Thus, the pump-beam intensity can be two orders of magnitude lower than is necessary with open-channel-dominated Feshbach molecules. We also demonstrate that the phase noise of the Raman lasers can be reduced by filter cavities, significantly improving the transfer efficiency.