Probing the collective excitations of a spinor polariton fluid
  We propose a pump-probe set-up to analyse the properties of the collective excitation spectrum of a spinor polariton fluid. By using a linear response approximation scheme, we carry on a complete classification of all excitation spectra, as well as their intrinsic degree of polarisation, in terms of two experimentally tunable parameters only, the mean-field polarisation angle and a rescaled pump detuning. We evaluate the system response to the external probe, and show that the transmitted light can undergo a spin rotation along the dispersion for spectra that we classify as diffusive-like. We show that in this case, the spin flip predicted along the dispersion is enhanced when the system is close to a parametrically amplified instability. 
M. Van Regemortel, M. Wouters, F. M. Marchetti
cond-mat.mes-hall