Loss of ultracold RbCs molecules via optical excitation of long-lived two-body collision complexes

We show that the lifetime of ultracold ground-state bosonic RbCs 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(6) ms in the dark. These results are crucial for further understanding of ultracold molecular collisions, and for benchmarking theoretical models.