Exciton-Polariton Lasing from Topologically Protected States

Thresholdless lasing is a long-sought goal for many applications. Yet, the inherent working principle behind lasers hinders its realization due to the necessity to reach population inversion. A new approach to overcome this limitation is based on exciton-polaritons. These hybrid light-matter excitations can undergo a phase transition to a coherent state, known as Bose-Einstein condensate, removing the requirement for population inversion.<br/><br/>The main limitation in achieving thresholdless exciton-polariton lasing is hindered by non-radiative and radiative losses that are inevitably present in microcavities. In this work we show the achievement of state-of-the-art polariton lasing threshold in a easy to fabricate GaAs/AlGaAs waveguide heterostructure. We focus on reducing the threshold by improving the fabrication technique to limiting exciton non-radiative channels, while at the same time we remove radiative losses using symmetry-protected bound states in the continuum (BIC). Furthermore, we will show how the topological properties of the condensate are transferred to the emitted light, giving rise to beam vortices in the far field.<br/><br/>In conclusion, this work unveils the possibilities introduced by dressed photons coupled to topologically protected states to realize low power and low cost coherent light sources.