The second and third order coherence functions $g^{ (n)}(0) (n=2 { \rm and} 3)$ of an exciton-polariton condensate is measured and compared to the theory. Contrary to an ideal photon laser, deviation from unity in the second and third order coherence functions is observed, thus showing a bunching effect, but not the characteristics of a standard thermal state with $g^{ (n)}(0)=n!$. The increase of bunching with the order of the coherence function, $g^{ (3)}(0) > g^{ (2)}(0)>1$, indicates that the polariton condensate is different from coherent state, number state and thermal state. The experimental results are in agreement with the theoretical model where polariton-polariton and polariton-phonon interactions are responsible for the loss of temporal coherence.
Categories: cond-mat.mes-hall cond-mat.other