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Cavity Quantum Electrodynamics with Quantum Dots

Confining both light and matter, discrete resonances of both are created, which is realised in optical resonators and in atoms or quantum dots, respectively.

By overlapping these resonances in space and frequency, their mutual coupling is enhanced compared to the case of light in free space. Spontaneous emission, a quantum electrodynamic effect, is enhanced by the enhanced density of states of photon modes. When the emission rate is surpassing the loss rate of the cavity photon mode, the spontaneously emitted photon is reabsorbed by the matter, and a new mixed photon and matter state is formed, the cavity polariton.

Apart from fundamental interest, these coupled states are important for quantum information and communication technology, as they show the ultimate strength of light-matter coupling, providing single photon switching and thus single photon logic.


We study the single-photon optical nonlinearities using ultrafast coherent nonlinear optical spectroscopy on individual optical resonators. We employ heterodyne spectral interferometry [1] to derive the fully complex nonlinear optical response, allowing to represent it in time and spectral domain.

In a two-level system strongly coupled to a cavity photon mode, a Jaynes-Cummings ladder is forming, which we demonstrated in a quantum dot  exciton coupled to a micropillar cavity [2].

The cavity mode can also be used to couple several excitons (which are quantum bits in QIP),  coherently, as we have shown in our recent work [3].


The project team

Project lead

Wolfgang Langbein

Professor Wolfgang Langbein

Head of Condensed Matter and Photonics Group