Optically-addressable spin qubits in silicon 28 – OCTOPUS

The OCTOPUS project aims at developing all the building blocks of an efficient spin-photon interface operating at telecom wavelengths in an isotopically-purified silicon 28 wafers, by investigating the magneto-optical properties of an isovalent carbon-related impurity, the so-called G-center. The OCTOPUS consortium comprises three partners with complementary expertises in growth, nanofabrication and spectroscopy: L2C-Montpellier (coordinator), CEA-Grenoble, and IM2NP-Marseille.

The G-center was originally highlighted in carbon-rich silicon samples undergoing high-energy irradiation followed by high temperature annealing. Thirty years ago, the goal was to grow silicon crystals as pure as possible, with intensive studies on impurities in silicon in order to remove them. After a brief renewal ten years ago in the context of laser emission in silicon photonic crystals, G-centers in silicon have remained unexplored for quantum technologies.

In this framework, a key feature of G-centers is their emission matching the important optical telecommunications wavelength O-band spreading between 1260-1360 nm. In addition, it was shown in the early 80's that the G-center has an electronic spin triplet state (S=1), which can be initialized by optical pumping and read-out through optical detection of the magnetic resonance using similar tools as the one commonly implemented nowadays to detect electron spins in solid-state systems by optical means. Finally, since July 2017, CEA-Grenoble (Partner 2 of the OCTOPUS consortium) is able to grow layers of isotopically pure silicon 28 by chemical vapour deposition, and is currently producing 28Si-on-insulator wafers using the SmartCut®process. Thanks to this strategic move, this partner is now at the forefront of the development of advanced quantum circuits on 28Si-on-insulator wafers. In the OCTOPUS project, CEA-Grenoble provides the clean quantum-grade environment required for taking advantage of the appealing properties of G-centers, in the prospect of building a spin-photon interface in silicon-based devices operating at telecom wavelengths.

With this technology in hand, the OCTOPUS project will make a major step forward in the comprehension and control of the basic properties of G-centers in silicon, as well as in the development of their far-reaching potential applications in quantum technologies. More specifically, the main goals of the project are:
i. to create individual G-centers through ion implantation in photonic nanostructures, which will provide an integrated single photon source in silicon emitting in the telecommunications wavelength range;
ii. to detect and control the electronic spin state of the G-center in isotopically purified silicon samples;
iii. to use the nuclear spin of the defect as a robust quantum memory.

This work will enable to assess the potential of G-center in silicon as a spin-photon interface operating at telecom wavelengths. As a matter of fact, the OCTOPUS ambition is to develop a disruptive quantum technology compatible with the two major markets of electronics and optical telecommunications. The OCTOPUS success will thus position our consortium at the forefront of the research on G-centers for silicon-based quantum technologies. Moreover, due to the long fabrication delays for CMOS quantum chips in silicon 28, OCTOPUS will likely be the first project to highlight the maturity of 28SiOI wafer fabrication at CEA-Grenoble. As such, OCTOPUS will strengthen the visibility of the French community in the context of the European Flagship initiative on Quantum Technologies.