An international team led by Technical University Munich (TUM) physicists Alexander Holleitner and Jonathan Finley has now succeeded in producing such quantum light sources in atomically thin material layers and placing them with nanometer precision.
First step towards the optical quantum computer"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, in order 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 precisely placed there.
Deterministic defectsThe physicists now used a layer of molybdenum disulphide (MoS2), only three atomic layers 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 flaws 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, with which such materials can be irradiated with an unprecedented local resolution, was of central technical importance.
On the way to novel light sourcesTogether 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 defects theoretically.
However, progress could be made not only in theory. Since the light sources are always based on the same defect in the material, they are basically indistinguishable. This enables applications based on the quantum mechanical principle of entanglement.
"Our quantum light sources can be very elegantly integrated into photonic circuits," says Klein. "Due to their high sensitivity, quantum sensors could be built for smartphones, for example, and extremely secure encryption technologies for data transmission could be developed.