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.

More information can be found in: Peter Cristofolini, Z. Hatzopoulos, Pavlos G. Savvidis, and Jeremy J. Baumberg,

“Generation of Quantized Polaritons below the Condensation Threshold.”
Phys. Rev. Lett.,
121(6), 067401 (2018).