  Exciton-polaritons (polaritons herein) offer a unique nonlinear platform for
studies of collective macroscopic quantum phenomena in a solid state system.
Shaping of polariton flow and polariton confinement via potential landscapes
created by nonresonant optical pumping has gained considerable attention due to
the degree of flexibility and control offered by optically-induced potentials.
Recently, large density-dependent energy shifts (blueshifts) exhibited by
optically trapped polaritons at low densities, below the bosonic condensation
threshold, were interpreted as an evidence of strong polariton-polariton
interactions [Nat. Phys. 13, 870 (2017)]. In this work, we further investigate
the origins of these blueshifts in optically-induced circular traps and present
evidence of significant blueshift of the polariton energy due to reshaping of
the optically-induced potential with laser pump power. Our work demonstrates
strong influence of the effective potential formed by an optically-injected
excitonic reservoir on the energy blueshifts observed below and up to the
polariton condensation threshold and suggests that the observed blueshifts
arise due to interaction of polaritons with the excitonic reservoir, rather
than due to polariton-polariton interaction.
