Newsportal - Ruhr-Universität Bochum
Novel quantum dots facilitate coupling to quantum memory systems
Researchers at the University of Basel and Ruhr-Universität Bochum have realised quantum dots – tiny semiconductor nanostructures – that emit light close to the red part of the spectrum with ultra-low background noise. Quantum dots might one day constitute the basis for quantum computers; the light particles, also called photons, would then serve as information carriers. Quantum dots with adequate optical properties had previously only been obtained for photons with wavelengths in the near-infrared range. Now, the researchers have succeeded in creating low-noise states at wavelengths between 700 and 800 nanometres, i.e. close to the visible red range. This would, for example, enable coupling to other photonic systems. They outline their findings in the journal “Nature Communications” from 21 September 2020.
Different wavelengths required
Systems for quantum communication require photons of different wavelengths. For communication over long distances, the main requirement is to avoid signal losses; wavelengths around 1,550 nanometres can be used for this purpose. For short distances, on the other hand, photons are needed that can be detected as effectively as possible and connected to other quantum memory systems. This would be possible with red light, or more precisely with wavelengths between 700 and 800 nanometres. Currently available photon detectors have their highest sensitivity in this range. Moreover, light particles of this frequency could be coupled with a rubidium storage system.
In order for information in a quantum system to be precisely encoded, manipulated and read out, stable optical emission is crucial. This is exactly what the researchers have now achieved for photons near the visible red range.
Lower aluminium content is the key to success
The project was a collaborative venture between a team of young physicists led by Professor Richard Warburton from the Basel-based Nano-Photonics Group and Professor Andreas Wieck, Dr. Arne Ludwig, Dr. Julian Ritzmann and colleagues from the Chair for Applied Solid State Physics in Bochum. The researchers converted the quantum dots in a semiconductor made of gallium arsenide. Since the system has to be cooled with liquid helium, it operates at low temperatures of minus 269 degrees Celsius.
One of the main challenges was to design a diode with gallium-arsenide quantum dots that reliably emits photons at these low temperatures. The Bochum-based team produced aluminium-gallium-arsenide layers with a lower aluminium concentration than usual, which improved the layers conductivity and stability. The Nano-Photonics team then used this material for the experiments in Basel.
Coupled system in progress
In the next step, the researchers are planning to combine the newly developed quantum dots with a rubidium quantum memory device. Such hybrid structures would be a first step towards practical applications in future quantum communication network.
The project was funded by the European Union as part of the Horizon 2020 Programme (Marie Skłodowska-Curie Grants no. 721394/4PHOTON and 840453/HiFig), by the Swiss National Science Foundation as part of the National Centre of Competence Research QSIT and the project with the funding number 200020_156637, the German Research Foundation as part of the projects at Collaborative Research Centre/Transregio 160 and project 383065199, the Franco-German University in the project DFH/UFA CDFA05-06, as well as the Federal Ministry of Education and Research (Q.Link.X 16KIS0867).
Liang Zhai, Matthias C. Löbl, Giang N. Nguyen, Julian Ritzmann, Alisa Javadi, Clemens Spinnler, Andreas D. Wieck, Arne Ludwig, Richard J. Warburton: Low-noise GaAs quantum dots for quantum photonics, in: Nature Communications, 2020, DOI: 10.1038/s41467-020-18625-z
Chair for Applied Solid State Physics
Faculty of Physics and Astronomy
Dr. Arne Ludwig
Phone: +49 234 32 25864
Dr. Julian Ritzmann
Phone: +49 234 32 25805
Prof. Dr. Andreas Wieck
Phone: +49 234 32 26726
Department of Physics
University of Basel
Prof. Dr. Richard Warburton
Phone: +41 61 207 3560
Phone: +41 61 207 3866
12 November 2020