  Phonon damping is the main source of pure dephasing in the solid state,
limiting many fundamental quantum effects to low temperature observations. Here
we show how excitons in semiconductors can be totally decoupled from the phonon
bath, even at room temperature, thanks to their strong interaction with
photons. To do so, we investigated ZnO microwires, a new semiconductor
nanostructure made of large band-gap material where the light can be trapped
and guided into whispering gallery modes. In this system, the very large
coupling regime between exciton and photon results in unusual exciton-polariton
of one-dimensional character and Rabi splitting as large as 300meV. We find
that polariton modes of excitonic fraction up to 75% exhibit no thermal
broadening up to room temperature. We show that this remarkable behavior is due
to the very large Rabi splitting as compared to the LO phonon energy.
