Higher order coherence of exciton-polariton condensates

Abstract

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.Comment: 4 pages, 4 figure

Temperature Dependence of Highly Excited Exciton Polaritons in Semiconductor Microcavities

“…Therefore, even though the time resolution of the detectors is greater than the PL lifetime, the detection system correctly collects the photon statistics. 25,30 If the actual correlation time is shorter than the pulse duration, then the g (2) (0) obtained underestimates its true value, 25 and in fact, even if the measured results do not reflect the true statistics, they still indicate the bunching and the difference from photon lasing that occurs far above the threshold (see Appendix B for more details).…”

“…In the 8 K case [ Fig. 8 (a)], the PL showed bunching behavior above the threshold (g (2) (0) > 1) 4,17,18,25,30 up until the high-excitation-density regime, which was more than a hundred times the condensation threshold (>300 mW). When the measurements were performed using a high-time-resolution streak camera, 17 the g (2) (0) below the threshold was closer to 2 after the statistics of the thermal state were correctly obtained.…”

“…30 The coherent state exhibits the all-order coherence g (n) (0) = 1, while the thermal state exhibits g (3) (0) = 6 > g (2) (0) = 2 > 1. Consequently, the statistics of the PL from the polariton condensate indicate that the condensate is not in the coherent state but close to the thermal distribution state.…”

“…17,18,30 The intensity correlation time of the system covers or is closer to the entire PL pulse. Therefore, even though the time resolution of the detectors is greater than the PL lifetime, the detection system correctly collects the photon statistics.…”

Steady-state generation of negative-Wigner-function light using feedback

“…We note that we make the standard assumption that the quantum statistics of the polaritons is the same as the light emerging from the microcavity, as this is a coherent process conserving momentum and energy [25]. This has been used to measure polariton correlation functions successfully [48].…”