Loss of Ultracold Rb 87 Cs 133 Molecules via Optical Excitation of Long-Lived Two-Body Collision Complexes

Abstract

We show that the lifetime of ultracold ground-state Rb87Cs133 molecules in an optical trap is limited by fast optical excitation of long-lived two-body collision complexes. We partially suppress this loss mechanism by applying square-wave modulation to the trap intensity, such that the molecules spend 75% of each modulation cycle in the dark. By varying the modulation frequency, we show that the lifetime of the collision complex is 0.53±0.06 ms in the dark. We find that the rate of optical excitation of the collision complex is 3-2+4×103 W-1 cm2 s-1 for λ=1550 nm, leading to a lifetime of <100 ns for typical trap intensities. These results explain the two-body loss observed in experiments on nonreactive bialkali molecules.