  In condensed-matter physics, remarkable advances have been made with atomic
systems by establishing a thorough control over cooling and trapping
techniques. In semiconductors, this method may also provide a deterministic
approach to reach the long standing goal of harnessing collective quantum
phenomena with exciton gases. While long-lived excitons are simply cooled to
very low temperatures using cryogenic apparatus, engineering confining
potentials has been a challenging task. This degree of control was only
achieved recently with devices realized by highly demanding nano-fabrication
processes. Here, we demonstrate an alternative to this technology and show how
a proper optical excitation allows to manipulate in-situ the exciton transport.
Our approach is based on the optically controlled injection and spatial
patterning of charges trapped in a field-effect device. Thus, electric field
gradients are created and implement microscopic traps or anti-traps for the
excitons dipole. Accordingly, any confinement geometry can be realized by
shaping the spatial profile of a laser excitation. Hence, we succeed in
trapping exciton gases in a density range where quantum correlations are
predicted at our very low bath temperature.
