  We perform quantum tomography on one-dimensional polariton condensates,
spontaneously occurring in linear disorder valleys in a CdTe planar microcavity
sample. By the use of optical interferometric techniques, we determine the
first-order coherence function and the amplitude and phase of the order
parameter of the condensate, providing a full reconstruction of the single
particle density matrix for the polariton system. The experimental data are
used as input to theoretically test the consistency of Penrose-Onsager
criterion for Bose-Einstein condensation in the framework of nonequilibrium
polariton condensates. The results confirm the pertinence and validity of the
criterion for a non equilibrium condensed gas.
