Two-color second-order correlations of the light scattered near-resonantly by a quantum dot were measured by means of spectrally-filtered coincidence detection. The effects of filter frequency and bandwidth were studied under monochromatic laser excitation, and a complete two-photon spectrum was reconstructed. In contrast to the ordinary one-photon spectrum, the two-photon spectrum is asymmetric with laser detuning and exhibits a rich structure associated with both real and virtual two-photon transitions down the "dressed states" ladder. Photon pairs generated via virtual transitions are found to violate the Cauchy-Schwartz inequality by a factor of 60. Our experiments are well described by the theoretical expressions obtained by del Valle et al. via time-and normally-ordered correlation functions.
@article{arxiv.1501.00898,
title = {Two-Color Photon Correlations of the Light Scattered by a Quantum Dot},
author = {M. Peiris and B. Petrak and K. Konthasinghe and Y. Yu and Z. C. Niu and A. Muller},
journal= {arXiv preprint arXiv:1501.00898},
year = {2015}
}