Abstract

In atom physics a superradiant nearly photon-less laser has been reported [1]. Also radiative life time changes for semiconductor quantum dots (QD) are known to be caused by superradiant coupling [2]. However, in former theoretical descriptions of semiconductor QD based microcavity lasers e. g. [3], the superradiant coupling between the different QDs is typically not included. We study the influence of radiation induced coupling between semiconductor QDs in a microcavity and its effect on the input/output characteristics and the lasing threshold. The input/output curves for a microcavity laser shown in Fig. 1 (a) reveal that superradiant coupling has a strong impact on the light intensity hb^†bi. The suppression of photon emission below the threshold and the enhancement above increases the height of the intensity jump at threshold. The intensity jump is commonly used to estimate the fraction of spontaneous emission into the laser mode (β-factor). Using a rate- or master-equation approach to describe this sample, one would underestimate the β-factor by about one order of magnitude. For a measure of the radiative coupling we define the cooperativity factor $C_F=\frac{{}^{〈b^{†}〉}\text{rad}\text{.coupled QDS}}{{}^{〈b^{†}〉}\text{independent QDS}}-1$ which is also shown in Fig. 1 (a). To systematically include correlations between individual QDs [4] and take the semiconductor properties of the QDs into account [5] we introduce a method termed Configuration Cluster Expansion. Having access to different levels of approximation, we are able to directly monitor the effect of QD-QD correlations.

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