B. Lounis, H. A. Bechtel, D. Gerion, P. Alivisatos, and W. E. Moerner, Chem. Phys. Lett., in press

We investigate the fluorescence intensity correlation function of a single CdSe quantum dot using a start-stop experiment. We observe strong photon antibunching, a signature of non-classical light emission, over a large range of intensities (0.1-100 kW/cm2). The lack of coincidence at zero time delay indicates a highly efficient Auger ionization process, which suppresses multi-photon emission in these colloidal quantum dots. Using careful analysis of the saturation behavior of the coincidence histograms, the absorption cross section of a single quantum dot has also been derived.

Figure 1: Histogram of time delays between consecutive photon pairs (which is proportional to the intensity correlation function) detected from the fluorescence of a single CdSe QD. The time bin size is 0.2 ns, the excitation intensity is 11 kW/cm2, and the accumulation time is 430 s. The histogram shows a dip that approaches zero (actual value~3) at zero time delay, which is a clear signature of photon antibunching. The solid line represents a single exponential fit with a rise time constant of 16 (±1) ns.