Photonic crystal cavity. The refractive index of a silicon waveguide is modulated by etching nano-scale holes. Thus, the emission of erbium dopants in the resonator can be dramatically enhanced.

Our group follows two different approaches to realize quantum networks with individual Erbium ions. In the second approach, we build on the mature platform of silicon nano-photonics in order to fabricate an efficient quantum interface between individual photons and single erbium dopants. In contrast to related experiments with other host crystals (Dibos et al. Phys. Rev. Lett. 120 (2018), Kindem et al. Nature 580 (2020)), in our approach the dopants are integrated directly into the silicon material. In a pioneering work, we have shown that the optical coherence in nanophotonic structures is at a par with other established hosts (arXiv:2005.01775 (2020)). This opens the door for scalable quantum memories fabricated by standard processes of the semiconductor industry.

We have recently fabricated nanophotonic resonators, as shown in the image, in which we achieve a quality factor exceeding 105 and a mode volume that is smaller than a cubic wavelength. We expect that this will enhance the emission of individual erbium dopants by four orders of magnitude. We aim to use the resulting fast light-matter coupling in order to demonstrate a novel, scalable platform for distributed quantum computing and quantum networking based on spin-photon quantum gates (Reiserer et al., Nature 508, (2014)).

To this end, our current efforts are focused on further improving the fabrication procedure and the coupling to these resonators, as well as tuning them in resonance with individual Erbium emitters. Our first publication in that field of study is: Weiss, Gritsch, Merkel & Reiserer: Erbium dopants in silicon nanophotonic waveguides. arXiv:2005.01775 (2020).

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