  Topological concepts have been applied to a wide range of fields in order to
successfully describe the emergence of robust edge modes that are unaffected by
scattering or disorder. In photonics, indications of lasing from topologically
protected modes with improved overall laser characteristics were observed.
Here, we study exciton-polariton microcavity traps that are arranged in a
one-dimensional Su-Schrieffer-Heeger lattice and form a topological defect mode
from which we unequivocally observe highly coherent polariton lasing.
Additionally, we confirm the excitonic contribution to the polariton lasing by
applying an external magnetic field. These systematic experimental findings of
robust lasing and high temporal coherence are meticulously reproduced by a
combination of a generalized Gross-Pitaevskii model and a Lindblad master
equation model. Thus, by using the comparatively simple SSH geometry, we are
able to describe and control the exciton-polariton topological lasing, allowing
for a deeper understanding of topological effects on microlasers.
