  Many experimental platforms for quantum science depend on state control via
laser fields. Frequently, however, the control fidelity is limited by optical
phase noise. This is exacerbated in stabilized laser systems where
high-frequency phase noise is an unavoidable consequence of feedback. Here we
implement an optical feedforward technique to suppress laser phase noise in the
STIRAP state transfer of ultracold RbCs molecules, across 114 THz, from a
weakly bound Feshbach state to the rovibrational ground state. By performing
over 100 state transfers on single molecules, we measure a significantly
enhanced transfer efficiency of 98.7(1)% limited only by available laser
intensity.
