Effect of optically induced potential on the energy of trapped exciton polaritons below the condensation threshold

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 flexibility and control enabled 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 [Y. Sun et al., 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 blueshifts of the polariton energy due to reshaping of the optically induced potential with laser pump power. Our work demonstrates the 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.