Tailoring the potential landscape of room-temperature single-mode whispering gallery polariton condensate

A key point of exciton polaritons is real-time controllability of potential energy and its landscape due to the hybrid nature of excitons and photons. Although wide-bandgap semiconductors allow us to generate room-temperature polaritons, unintentional localizations of two-dimensional cavities caused by disorder (dephasing and potential fluctuation) still hinder the establishment of ballistic extensions of polariton condensates. This ballistic extension accompanies spatial coherence, an essential factor for phase transitions as well as any quantum controls. Here we propose a room-temperature polariton system with ultralow disorder capable of one-dimensional ballistic propagation. Selectively grown GaN wire dramatically reduces disorder in both the exciton perspective via dislocation bending and the photon perspective through crystallographically defined hexagonal cavities. This high-quality wire on a substrate forms triangular whispering gallery modes and allows us to demonstrate the room-temperature single-mode one-dimensional polariton condensate with ballistic propagation. This ballistic propagation is manipulated by active real-time control of the potential gradient. The correlation between propagation distances deduced from real and momentum space provides strong evidence of ballistic propagations in an ultralow-disordered one-dimensional system.