Abstract
We count a small number of atoms trapped in an optical microtrap, using fluorescence induced by a standing wave of blue-detuned light. Blue-detuned light limits losses from light-assisted collisions, allowing us to manipulate the trapped atoms further. When a pair of trapped atoms is detected in this way, we apply a tailored laser light pulse to induce light assisted-collisions. We directly observe that these collisions lead to either one or both atoms being lost from the microtrap. By optimizing the frequency and intensity of the laser beam inducing the light-assisted collisions, one atom loss can be made to dominate over pair loss. We demonstrate that in a microtrap occupied by similar to 50 atoms, this optimized light-assisted collision pulse can eject all but one atom efficiently. This method may be used to prepare many singly occupied microtraps for a neutral atom based quantum computation device.