  We investigate experimentally one of the main features of a quantum fluid
constituted by exciton polaritons in a semiconductor microcavity, that is
quantum degeneracy of a macroscopic fraction of the particles. We show that
resonant pumping allows to create a macroscopic population of polaritons in one
quantum state. Furthermore we demonstrate that parametric polariton scattering
results in the transfer of a macroscopic population of polariton from one
single quantum state into another one. Finally we briefly outline a simple
method which provides direct evidence of the first-order spatial coherence of
the transferred population.
