Optical cycling in polyatomic molecules with complex hyperfine structure

We have developed and demonstrated a scheme to achieve rotationally closed photon cycling in polyatomic molecules with complex hyperfine structure and sensitivity to hadronic symmetry violation, specifically, ¹⁷¹YbOH and ¹⁷³YbOH. We calculate branching ratios for spontaneous decay into the different hyperfine levels and identify repumping schemes. We demonstrate our scheme by cycling photons in a molecular beam and verify that we have achieved rotationally closed cycling by measuring optical pumping into unaddressed vibrational states. Our work makes progress along the path toward utilizing photon cycling for state preparation, readout, and laser cooling in precision measurements of polyatomic molecules with complex hyperfine structure.