Improving the stimulated Raman adiabatic passage efficiency for ultracold 6Li40K ground state molecules

Abstract Ultracold polar molecules represent a rapidly advancing platform at the forefront of quantum simulation, quantum computation, quantum chemistry, and precision measurement. We report an experimental investigation for improving the creation efficiency of ultracold 6 Li 40 K ground state molecules using stimulated Raman adiabatic passage (STIRAP). We address laser amplitude/phase noise and polarization impurity to improve STIRAP efficiency. The phase noise of our two Raman lasers is suppressed effectively by extending the cavity length for the external-cavity diode lasers (ECDLs). Further, we find that even a weak polarization impurity significantly reduces the STIRAP efficiency on the single-photon resonance (Δ = 0) for 6 Li 40 K, due to coupling to undesired molecular levels. However, STIRAP efficiencies over 90% can be achieved by increasing Δ/2 π to 10 MHz, which is comparable to the excited-state scattering rate. Our work holds significance for achieving efficient STIRAP transfer in ultracold molecules with unresolved excited-state hyperfine splittings and large scattering rates.