Quantum light sources pave the way to optical circuits
Current integrated circuits rely on electrons as information carriers. In the future, photons, which transmit information in optical circuits, could also take on this task. The basic building blocks of such novel chips are quantum light sources, which are then connected to quantum optical waveguides and detectors. An international team led by Alexander Holleitner and Jonathan Finley, physicists at the Technical University of Munich (TUM), has now succeeded in producing such quantum light sources in atomically thin material layers and placing them with nanometer precision.
“This represents an important first step towards optical quantum computers,” says Julian Klein, first author of the study. “For future applications, the light sources must be coupled to photonic circuits, such as waveguides, to enable light-based quantum calculations. The decisive factor here is precise and precisely controllable placement of the light sources. In conventional three-dimensional materials such as diamond or silicon, there are also active quantum light sources, but they cannot be placed there precisely enough.
The physicists used a layer of molybdenum disulfide (MoS2) semiconductor, only one atomic layer thick, as the starting material. They irradiated it with a helium ion beam, which they focused on an area of less than one nanometer. In order to produce optically active defects, the desired quantum light sources, molybdenum or sulfur atoms are selectively removed from the layer. The defects are traps for so-called excitons, electron-hole pairs that then emit the desired photons.
The new helium-ion microscope at the Center for Nanotechnology and Nanomaterials at the Walter Schottky Institute of the Technical University of Munich played a major role in this, allowing such materials to be irradiated with a previously unattained local resolution.
Together with theoreticians from the TUM, the Max Planck Society and the University of Bremen, the team developed a model to describe the observed energy states of the flaws theoretically.
In the future, the researchers also want to generate more complex light source patterns, for example in lateral two-dimensional lattice structures of excitons, in order to investigate many-particle phenomena or exotic material properties.
However, progress could be made not only in theory, but also with regard to possible technical developments. Since the light sources are always based on the same defect in the material, they are in principle indistinguishable. This enables applications based on the quantum mechanical principle of entanglement.
The quantum light sources can be elegantly integrated into photonic circuits. This could be used, for example, to build quantum sensors for smartphones and to develop extremely secure encryption technologies for data transmission.
Further information:
https://www.wsi.tum.de/views/sub_group.php?group=Holleitner
https://www.wsi.tum.de/views/groups.php?group=finley
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