Generation of Quantized Polaritons below the Condensation Threshold

Exciton polaritons in high quality semiconductor microcavities can travel long macroscopic distances (>100 μm) due to their ultralight effective mass. The polaritons are repelled from optically pumped exciton reservoirs where they are formed; however, their spatial dynamics is not as expected for pointlike 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 delocalized quantum particles, even before they form Bose condensates.