Press release 099:  Copyright:

Date: November 30, 2016, No. 099

Auf dem Weg zu idealen Einzelphotonen

Integrating quantum dots and atomic vapors

A joint research team of the University of Stuttgart and the Max Planck institute for solid state research has recently performed an experiment which combines the state-of-the-art research on quantum dots and atomic vapors. The work, led by the scientists Ilja Gerhardt (3 rd Institute of Physics, University of Stuttgart and MPI) and Simone Luca Portalupi (Institute of semiconductor optics and functional interfaces – IHFG, University of Stuttgart), aims to integrate the ideal properties of solid-state based single photon sources, which are spectrally aligned to an atomic transition.

The quantum dot single-photon source is specially selected from an in-house grown sample to match exactly the resonance of atomic cesium vapor. Under strong coherent resonant excitation, the emission is split into a so-called Mollow-triplet, which emits light distributed on three distinct spectral lines. The optical emission emits the photons one by one, unlike a light bulb or e.g. the sun. These non-classical single photon sources can be extremely narrow-band and extremely bright, and open the opportunity for quantum communication and quantum information protocols.

A fundamental requirement for interfacing different, distant sources is currently challenging due to different linewidth and color of the solid-state-based single photon sources. The current work aims to face this challenge, producing photons which are precisely set in energy, meaning that they can be effectively used in the realization of quantum repeaters.

As a matter of fact the atomic vapor is also used as the primary time standard in industry. Here it is used as a Faraday filter to precisely select specific lines from the quantum dots, which are emitting bright and high quality single photons. The atoms act as a special frequency reference and extremely narrow-band filter. Their exact color, in scientific terms their spectral linewidth, is many thousand times narrower than e.g. some normal colored dye.

The presented research is along the line of quantum hybrid systems, and aims to integrate the work usually performed by different research teams: the vision being the integration of solid-state quantum optics and atomic spectroscopy onto a unified platform. In future such research will enable novel quantum technologies, such as secure remote communications and precision measurements, which utilize the quantum properties of nature to enhance sensitivity and set new precision standards.

The work was recently published in Nature Communications:

Simone Luca Portalupi, Matthias Widmann, Cornelius Nawrath, Michael Jetter, Peter Michler, Jörg Wrachtrup, and Ilja Gerhardt, “Simultaneous Faraday filtering of the Mollow triplet sidebands with the Cs-D1 clock transition”, Nature Communications 7, 13632 (2016), doi:10.1038/ncomms13632 2016).

Dr. Simone Luca Portalupi, Universität Stuttgart, Institut für Halbleiteroptik und Funktionelle Grenzflächen, Tel. ++49 (0)711 685 65226, E-Mail

Dr. Ilja Gerhardt, Universität Stuttgart, 3. Physikalisches Institut und Max Planck Institut für Festkörperforschung, Tel. ++49 (0)711 685 65283 E-Mail:


The quantum dot single-photon source is specially selected from an in-house grown sample to match exactly the resonance of atomic cesium vapor.