ArXiv · 2026
Ian N. Hammock (Pritzker School of Molecular Engineering, University of Chicago, Chicago, USA), Kinfung Ngan (JILA and Department of Physics, University of Colorado Boulder, Boulder, USA), Antoni W. Wellisz (Pritzker School of Molecular Engineering, University of Chicago, Chicago, USA), Keira Linder (Pritzker School of Molecular Engineering, University of Chicago, Chicago, USA), Midrel Wilfried Ngandeu Ngambou (Materials Science Division and Center for Molecular Engineering, Argonne National Laboratory, Lemont, USA, Q-NEXT, Argonne National Laboratory, Lemont, USA), Jiefei Zhang (Pritzker School of Molecular Engineering, University of Chicago, Chicago, USA, Q-NEXT, Argonne National Laboratory, Lemont, USA), Xinghan Guo (Pritzker School of Molecular Engineering, University of Chicago, Chicago, USA), Benjamin Pingault (Pritzker School of Molecular Engineering, University of Chicago, Chicago, USA, Q-NEXT, Argonne National Laboratory, Lemont, USA), Shuo Sun (JILA and Department of Physics, University of Colorado Boulder, Boulder, USA), David D. Awschalom (Pritzker School of Molecular Engineering, University of Chicago, Chicago, USA, Department of Physics, University of Chicago, Chicago, USA), F. Joseph Heremans (Pritzker School of Molecular Engineering, University of Chicago, Chicago, USA, Q-NEXT, Argonne National Laboratory, Lemont, USA), Alexander A. High (Pritzker School of Molecular Engineering, University of Chicago, Chicago, USA, Materials Science Division and Center for Molecular Engineering, Argonne National Laboratory, Lemont, USA), Nazar Delegan (Pritzker School of Molecular Engineering, University of Chicago, Chicago, USA, Q-NEXT, Argonne National Laboratory, Lemont, USA)
Group IV color centers in diamond – silicon, germanium, tin, and lead-vacancy centers – are a promising platform for quantum networking. Typical Group-IV creation utilizes ion implantation during diamond growth that leaves the color centers with a broad depth distribution and damage-induced strain inhomogeneity. Deterministic placement and damage reduction in Group IV generation are essential for improving this platform. In this letter, we report on the localization of germanium-vacancy (GeV⁻) to a < 10 nm layer via the timed injection of GeH₄ during microwave plasma chemical vapor deposition. In this layer we have realized 17 ppm of Ge and a strain-free environment for the GeV⁻. Subsequent electron irradiation and annealing have generated a sheet density of 0.12 GeV⁻/μm². The minimal damage from color center generation mitigates spectral inhomogeneity and allows spectral resolution of isotopic clusters, with the best cluster having an inhomogeneous distribution of 2.14 GHz and an average linewidth of 47 ± 11 MHz. Our study gives insight into formation dynamics of GeV⁻ in delta-doped systems and estimates our vacancy to GeV⁻ yield to be ≥ 90%, establishing an athermal nearest-neighbor formation model. We further characterized the spin T₂^* and set a lower bound of 730 ns, limited by a paramagnetic defect.
