Silicon nanopillaries for quantum communication

Researchers use an objective lens to test the light output from a series of silicon nanopillaries on a chip. Credit: HZDR / Juan Baratech

Around the world, specialists are working to implement quantum information technologies. One important path involves light: Looking to the future, individual light packets, also known as light quanta or photons, could transmit both encoded and actually touch-proof data. To this end, new photon sources are needed that emit single quanta of light in a controlled manner and on demand. It has only recently been discovered that silicon can 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 now presented an appropriate manufacturing technology using silicon nanopillaries: a chemical etching method followed by ion bombardment. Their research is published in Journal of Applied Physics.

“Silicon and single photon sources in the telecommunications field have long been the missing link in accelerating the development of quantum communication via optical fibers. Now we have created the necessary preconditions,” explains Dr. Yonder Berencén of the HZDR Institute of Physics and Ion Beam Materials Research who conducted the current study. Although single photon sources have been fabricated from materials such as diamonds, only silicon-based sources generate particles of light at the right wavelength to proliferate in optical fibers, a considerable advantage for practical purposes.

The researchers achieved this technical breakthrough by choosing a wet etching technique, what is known as MacEtch (metal-assisted chemical etching), rather than conventional dry etching techniques for processing silicon on a chip. These standard methods, which allow for the creation of photonic silicon structures, use highly reactive ions. These ions induce light emission defects caused by radiation damage in the silicon. However, they are randomly distributed and overlap the desired optical signal with the noise. Metal-assisted chemical etching, on the other hand, does not generate these defects, but 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 initially fabricated the simplest form of a potential light-wave guide structure: silicon nanopillars on a chip. They then bombarded the finished nanopillaries with carbon ions, just as they would a huge block of silicon, thus generating 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. For every square millimeter of chip, thousands of silicon nanopillaries conduct and group the light from the sources by directing it vertically through the pillars.

The researchers varied the diameter of the pillars because “we hoped this meant that we could create a single defect on thin pillars and actually generate a single photon source per pillar,” explains Berencén. “It didn’t work perfectly the first time. By comparison, even for the thinnest pillars, the dose of our carbon bombardment was too high. But now the step to single photon sources is short.”

This is a step the team is already working hard on because the new technique has also sparked a kind of rush for future applications.

“My dream is to integrate all the basic building blocks, from a single photon source via photonic elements to a single photon detector, on a single chip and then connect many chips via commercial optical fibers to form a modular quantum network.” Berencen states.

Single photons from a silicon chip

More information:
Michael Hollenbach et al, metal-assisted chemically etched silicon nanopillaries housing telecommunication photon emitters, Journal of Applied Physics (2022). DOI: 10.1063 / 5.0094715

Michael Hollenbach et al, Engineering of single photon emitters in silicon for scalable quantum photonics, Express Optics (2020). DOI: 10.1364 / OE.397377

Provided by the Helmholtz Association of German Research Centers

Citation: Silicon nanopillars for quantum communication (2022, September 20) recovered on September 22, 2022 from

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