Cold atom-semiconductor hybrid quantum system

Lucas Béguin, Fei Ding, Aline Faber, Jan-Philipp Jahn, Andreas Jöckel, Tobias Kampschulte, Andreas Kuhlmann, Mathieu Munsch, Armando Rastelli, Nicolas Sangouard, Oliver G. Schmidt, Philipp Treutlein and Richard J. Warburton

Universität Basel, Switzerland
IFW Dresden, Germany
Johannes-Kepler University, Linz, Austria

Our hybrid project aims at storing single photons emitted by semiconductor quantum dots (QDs) into a cold atomic ensemble. Indeed, semiconductor QDs are excellent single-photon sources that enable triggered emission at a high rate with high spectral purity. Independently, atomic ensembles have emerged as one of the best memories for single photons, providing high efficiency storage and long memory lifetimes. In this project, we combine these two disparate physical systems to exploit the best features from both worlds. On the one hand, we have characterized a new type of self-assembled GaAs quantum dots that emit Fourier transform limited single-photons (Δ𝜈 = 1.5 GHz) at a wavelength compatible with Rb atoms. Fine-tuning of the photon frequency is achieved via strain. This allowed us to perform a spectroscopy of the Rb D2-line at the single-photon level in the Rayleigh scattering regime, proving that we can address the different hyperfine transitions. On the other hand, we have developed a detailed theory of an EIT-based memory scheme in a dense ultracold ensemble of 87Rb atoms (OD>150). In the long term, such a memory will form the basis for experiments on hybrid entanglement and quantum networks.