(color online) Preparation of single atom in optical microtrap. (a) Stochastic loading of atoms in a microtrap from MOT. (b) Histogram displays the 0-atom, 1-atom, and N-atom peaks. The distribution of atom number in the steady state is governed by light-assisted collisions and random one-body events. (c) and (d) Feedback protocol for a single-atom preparing. The 0-atom and N-atom peaks are clearly missing. Both histograms correspond to a total of about 10000 counting samples.