Exciton polaritons in high quality semiconductor microcavities can travel long macroscopic distances (>100ฮผm) due to their ultra-light effective mass. The polaritons are repelled from the optically-pumped exciton reservoirs where they are formed, however their spatial dynamics is not as expected for point-like particles. Instead we show polaritons emitted into waveguides travel orthogonally to the repulsive potential gradient, and can only be explained if they are emitted as macroscopic delocalised quantum particles, even before they form Bose condensates
