Germanium color center in diamond for nanophotonic and sensing applications - Alexey Akimove

Color centers in diamond attract a lot of attention due to unique properties of diamond, such its optical and chemical purity, low concertation of nuclear spins in diamond matrix and also its physical and chemical inertness. Nitrogen vacancy (NV) color centers in diamond is the most studied color center in diamond because its fluorescence rate does depend on spin state this way enabling readout of the spin state. This property opens a lot of opportunities to for it implementation in quantum information processing [1] and sensing [2] applications. Nevertheless, NV color center has number of important disadvantages, such as broad emission spectrum dominated by phonons sideband with only 5% emission in zero-phonon sideband. Another problem is its high sensitivity to surface and structural defects in diamond often introduced by surrounding nanostructures. These disadvantages stimulated search for other color centers, which would have narrow spectrum dominated by zero-phonon line and better behavior in nanostructures.

The silicon-vacancy (SiV) center was suggested as such a center. Due to high symmetry of this center, it does not have dipole moment in the ground state and therefore is not as sensitive to various surface defects and damages as NV center. Moreover, it happens to have narrow zero-phonon line dominating the spectrum. However, unfortunately, exited state decay of this center is dominated by non-radiative relaxation. The next natural candidate is germanium-vacancy (GeV) center since Ge is right under Si in the Mendeleev table. This color center is expected to have less non-radiative decay and therefore could be good replacement for SiV. The key advantage of the group IV color centers in diamond is there relatively low sensitivity to the damages, created by nanofabrication. This opens unique opportunity to use this color centers with nanostructures photonic. It been already successfully demonstrated, that SiV containing nanocavities may significant advance performance of the color centers, making many quantum information processing possible [3,4]. In or work we are trying to make the next step in the development for such a device by integrating nanodiamonds, containing GeV color center with photonics devices out of more conventional for industry materials.

Another application of GeV color center developed by my group is temperature sensing. Again, the absolute record in combination of special resolution and sensitivity in measurement of magnetic fields and temperature belong to NV color centers in diamond. But these measurements require use of microwave radiation of Watts level which somewhat limits its applications in bioscience. We found that GeV allow different, microwave-free all-optical way of temperature measurements which is already found some application in bio community.

References [1] M. W. Doherty, N. B. Manson, P. Delaney, F. Jelezko, J. Wrachtrup, and L. C. L. Hollenberg, Phys. Rep. 528, 1 (2013). [2] B. K. Ofori-Okai, S. Pezzagna, K. Chang, M. Loretz, R. Schirhagl, Y. Tao, B. A. Moores, K. Groot-Berning, J. Meijer, and C. L. Degen, Phys. Rev. B - Condens. Matter Mater. Phys. 86, (2012). [3] A. Sipahigil, R. E. Evans, D. D. Sukachev, M. J. Burek, J. Borregaard, M. K. Bhaskar, C. T. Nguyen, J. L. Pacheco, H. A. Atikian, C. Meuwly, R. M. Camacho, F. Jelezko, E. Bielejec, H. Park, M. Lončar, and M. D. Lukin, Science 354, 847 (2016). [4] D. D. Sukachev, A. Sipahigil, C. T. Nguyen, M. K. Bhaskar, R. E. Evans, F. Jelezko, and M. D. Lukin, Phys. Rev. Lett. 119, 223602 (2017).