Light-assisted collisions between a few cold atoms in a microscopic dipole trap

We study light-assisted collisions in an ensemble containing a small number (~3) of cold ⁸⁷Rb atoms trapped in a microscopic dipole trap. Using our ability to operate with one atom exactly in the trap, we measure the one-body heating rate associated with a near-resonant laser excitation, and we use this measurement to extract the two-body loss rate associated with light-assisted collisions when a few atoms are present in the trap. Our measurements indicate that the two-body loss rate can reach surprisingly large values β>10^-8 cm³ s^-1 and varies rapidly with the trap depth and the parameters of the excitation light.