Strong Coupling of Quantum Dots in Microcavities

We show that strong coupling (SC) of light and matter as it is realized with quantum dots in microcavities differs substantially from the paradigm of atoms in optical cavities. The type of pumping used in semiconductors yields new criteria to achieve SC, with situations where the pump hinders, or on the contrary, favors it. We analyze one of the seminal experimental observation of SC of a quantum dot in a pillar microcavity [Reithmaier et al., Nature (London) 432, 197 (2004)] as an illustration of our main statements.

Figure 1

Anticrossing of the cavity (C) and exciton (X) photoluminescence lines as reported by Reithmaier et al. [3], demonstrating SC in their system. Energies are given in meV. The gray (red) lines are our superimposed fits with the best global fit parameters in the top left corner. Such a good agreement cannot be obtained neglecting pumping.

Figure 2

(a) Regions of strong (blue) and weak (red) coupling at resonance in the space of parameters (${\gamma }_a$, $P_b$), with ${\gamma }_b\approx 2.3g$ and $P_a\approx 0.12{\gamma }_a$ fitting the experiment of Reithmaier et al. [3], marked by a plain blue point. Region 1 exhibits line splitting, while in the darker area 2, although still in SC, the splitting cannot be resolved. The dashed vertical line marks the criterion for SC in absence of pumping, giving rise to region 3, where SC is recovered (with line splitting) thanks to pumping, and region 4, where it is lost because of it. In the inset, the same but for $P_a=0$, in which case the line splitting of 3 would not be resolved. (b),(c) Spectra of emission with increasing exciton pumping $P_b$ marked by the hollow points in (a). For ${\gamma }_a=2g$ in (b), SC is retained throughout and made more visible. For the best fit parameter, ${\gamma }_a\approx 3.6g$ in (c), line splitting is lost increasing pumping, first because it is not resolved [region 2 of (a)], then because the system goes into WC [region 4 of (a)].