Light trapped in a photonic dot: Microspheres act as a cavity for quantum dot emission

Optical microcavities that confine the propagation of light in all three dimensions (3D) are fascinating research objects to study 3D-confined photon states, low-threshold microlasers, or cavity quantum electrodynamics of quantum dots in 3D microcavities. A challenge is the combination of complete electronic confinement with photon confinement, e.g., by linking a single quantum dot to a single photonic dot. Here we report on the interplay of 3D-confined cavity modes of single microspheres (the photonic dot states) with photons emitted from quantized electronic levels of single semiconductor nanocrystals (the quantum dot states). We show how cavity modes of high cavity finesse are switched by single, blinking quantum dots. A concept for a quantum-dot microlaser operating at room temperature in the visible spectral range is demonstrated. We observe an enhancement in the spontaneous emission rate; i.e., the Purcell effect is found for quantum dots inside a photonic dot.