  We report on noise-induced-spin-ordering in a collective quasipaticle system:
spinor stochastic resonance. Synergetic interplay of a polarization-modulated
signal and a polarization-noise allows us to switch coherently between the two
metastable states of a microcavity-polariton spin bistable system. Spinor
stochastic resonance is demonstrated in a zero-dimensional GaAs based
microcavity. The resonance behavior of both the spin amplification and the
signal-to-noise ratio are experimentally evidenced as a function of the noise
strength for different amplitude modulations. They are theoretically reproduced
using a spinor- Gross-Pitaevskii equation driven by a randomly polarized laser
field.
