Experts from all over the world are implementing quantum information technologies. One significant route uses light: In the future, single light packets, also referred to as light quanta or photons, may be able to transmit data that is both coded and practically tap-proof. To achieve this, new photon sources that emit single light quanta in a controlled manner and on demand are needed. The ability of silicon to support single-photon sources with characteristics suitable for quantum communication has only recently been discovered. But nobody has figured out how to incorporate the sources into contemporary photonic circuits to this point. A team led by the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) has now introduced a suitable production technique using silicon nanopillars using chemical etching followed by ion bombardment.
“The missing piece in accelerating the advancement of quantum communication over optical fibers has long been silicon and single-photon sources. We now have the prerequisites in place for it, “Dr. Yonder Berencén, the study’s principal investigator and director of the Institute of Ion Beam Physics and Materials Research at HZDR,” explains. Even though single-photon sources can be made from materials like diamond, only silicon-based sources produce light particles with the right wavelength for optical fiber propagation. This is a big advantage for real-world applications.
The wet etching method, known as MacEtch (metal-assisted chemical etching), was chosen by the researchers in place of the more traditional dry etching methods for processing silicon on a chip, and it led to this technological advancement. These common techniques, which enable the development of silicon photonic structures, make use of highly reactive ions. Because of the radiation damage to the silicon, these ions cause defects that emit light. But because of its random distribution, noise is added on top of the desired optical signal. Metal-assisted chemical etching, on the other hand, doesn’t cause these problems. Instead, the material is chemically removed while it is covered by a metal mask.
The goal: single photon sources compatible with the fiber-optic network.
Researchers first created silicon nanopillars on a chip using the MacEtch technique, which is the most basic form of a potential light wave-guiding structure. They created photon sources embedded in the finished nanopillars by bombarding them with carbon ions, just as they would with a large silicon block. The size, spacing, and surface density of the nanopillars can be precisely manipulated and adjusted to be compatible with contemporary photonic circuits by using the new etching method. The light from the sources goes vertically through thousands of silicon nanopillars on a square millimeter chip, which guide and bundle the light.
We had hoped that this would allow us to perform single defect creation on thin pillars and actually generate a single photon source per pillar, which is why the researchers changed the diameter of the pillars. “The first time, it didn’t function perfectly. Our carbon bombardment was too high in comparison, even for the thinnest pillars. Single photon sources, however, are now only a small step away.
A stage on which the team has already begun to put in a lot of effort because the new technique has also sparked a competition for potential applications. “My dream is to integrate all the fundamental building blocks, from a single photon source via photonic elements through to a single photon detector, on a single chip and connect many chips via commercial optical fibers to form a modular quantum network,” says Berencén.
