All over the world, specialists are working on the implementation of quantum information technologies. One important path involves light: in the future, single packets of light, also called light quanta or photons, could transmit data that is both encoded and effectively eavesdropped. To this end, new photon sources are needed to emit single quanta of light in a controlled manner and on demand. It was only recently discovered that silicon could host single photon sources with properties suitable for quantum communication. So far, however, no one has been able to integrate the sources into modern photonic circuits. For the first time, a team led by the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) has just presented a suitable production technology using silicon nanopillars: a chemical etching method followed by ion bombardment.
“Silicon and single photon sources in telecommunications have long been the missing link to accelerate the development of quantum fiber optic communication. We have now created the necessary preconditions for this,” says Dr. Yonder Berencén of HZDR’s Ion Research Institute. Beam Physics and Materials Research who led the current study. Although single-photon sources have been made of materials like diamond, only silicon-based sources generate light particles at the right wavelength to proliferate in optical fibers – a huge advantage for practical purposes.
The researchers achieved this technical breakthrough by choosing a wet etching technique – known as MacEtch (metal-assisted chemical etching) – rather than conventional dry etching techniques to process the silicon on a chip. These classical methods, which allow the creation of photonic structures in silicon, use highly reactive ions. These ions induce light emission defects caused by radiation damage in the silicon. However, they are randomly distributed and blanket the desired optical signal with noise. Metal-assisted chemical etching, on the other hand, does not generate these defects – instead, the material is chemically etched under a kind of metal mask.
The goal: single photon sources compatible with the fiber optic network
Using the MacEtch method, the researchers first fabricated the simplest form of a potential light waveguide structure: silicon nanopillars on a chip. They then bombarded the finished nanopillars with carbon ions, as they would a massive block of silicon, and thus generated photon sources embedded in the pillars. The use of the new etching technique means that the size, spacing and surface density of the nanopillars can be precisely controlled and adjusted to be compatible with modern photonic circuits. Per square millimeter of chip, thousands of silicon nanopillars conduct and gather the light from the sources by directing it vertically through the pillars.
The researchers varied the diameter of the pillars because “we hoped this would mean we could create a single defect on thin pillars and actually generate a single photon source per pillar,” says Berencén. “It didn’t work perfectly the first time. In comparison, even for the thinnest pillars, the dose of our carbon bombardment was too high. But now there is only one step towards single photon sources. »
A step on which the team is already working intensively because the new technique has also triggered a kind of race for future applications. “My dream is to integrate all the basic building blocks, from a single photon source via photonics to a single photon detector, on a single chip, and then connect many chips through commercial fiber optics to form a modular quantum network,” says Berencén.
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Materials provided by Helmholtz-Zentrum Dresden-Rossendorf. Note: Content may be edited for style and length.