  Large arrays of individually controlled atoms trapped in optical tweezers are
a very promising platform for quantum engineering applications. However, to
date, only disordered arrays have been demonstrated, due to the
non-deterministic loading of the traps. Here, we demonstrate the preparation of
fully loaded, two-dimensional arrays of up to 50 microtraps each containing a
single atom, and arranged in arbitrary geometries. Starting from initially
larger, half-filled matrices of randomly loaded traps, we obtain user-defined
target arrays at unit filling. This is achieved with a real-time control system
and a moving optical tweezers that performs a sequence of rapid atom moves
depending on the initial distribution of the atoms in the arrays. These results
open exciting prospects for quantum engineering with neutral atoms in tunable
geometries.
