  Coherent bosonic ensembles offer the promise of harnessing quantum effects in
photonic and quantum circuits. In the dynamic equilibrium regime, the
application of polariton condensates is hindered by exciton-polariton
scattering induced de-coherence in the presence of a dark exciton reservoir. By
spatially separating the condensate from the reservoir, we drive the system
into the weak interaction regime, where the ensemble coherence time exceeds the
individual particle lifetime by nearly three orders of magnitude. The observed
nanosecond coherence provides an upper limit for polariton self-interactions.
In contrast to conventional photon lasers, we observe an increased contribution
from the super-Poissonian component of the condensate to the overall particle
number fluctuations. Coupled with the recent emergence of a quantum regime in
polaritonics, coherence times extended to several nanoseconds favour the
realization of quantum information protocols.
