A spin coherence time exceeding seven hundred nanoseconds has been achieved in germanium-vacancy colour centres within diamond. These defects are created using timed injection of germane gas during diamond growth, avoiding the strain typically caused by ion implantation. Researchers pioneered a technique for creating germanium-vacancy centres within diamonds; these defects are promising components for future quantum technologies. This approach carefully introduces germanium during the growth process itself, unlike traditional methods using ion implantation which can damage the diamond and create inconsistencies.

This precise control yields fewer flaws and enables placement of the colour centres within an ultra-thin layer without introducing significant strain into the material’s structure. Traditionally, such colour centres were created using ion implantation, essentially firing ions into the diamond structure, often causing damage and inconsistencies.

Instead, this team carefully introduces germanium during the diamond’s growth process via microwave plasma chemical vapor deposition, a high-tech cooking process where gases break down with energy waves to build up layers on a surface. The resulting material boasts a sheet density of 0.12 GeV^-/μm^2, but what does that actually mean for its performance. Further details regarding these formation dynamics follow.

Germane gas injection creates high density germanium-vacancy centres with extended

Spin coherence times now exceed seven hundred nanoseconds in germanium-vacancy colour centres within diamond, an improvement over previous results limited to around several tens of nanoseconds. This precise control yields sheet densities of 0.12 GeV^-/μm^2, alongside minimal strain and allows isotopic resolution with inhomogeneous widths as low as 2.14GHz and linewidths averaging $47 pm $11 MHz.

Surpassing prior benchmarks capped at tens of nanoseconds, this represents major progress towards viable quantum technologies. Electron irradiation followed by annealing also generated a sheet density of 0.12 GeV^-/μm^2. Achieving isotopic resolution; the narrowest observed cluster displayed an inhomogeneous width of just 2.14GHz and average linewidths of $47 pm $11 MHz. While these results demonstrate excellent optical homogeneity and high vacancy yield, estimated at greater than ninety percent, the precise identity of the paramagnetic species limiting coherence or how to scale this process economically for large quantum devices remains unknown.

s Exhibit Long Coherence Despite Unidentified Paramagnetic Impurity

Creating germanium-vacancy centres within a ten nanometre layer is key towards viable quantum technologies, as conventional ion implantation introduces damaging strain that hinders performance and scalability. Despite achieving times exceeding seven hundred nanoseconds, pinpointing the source of limited spin coherence, a “paramagnetic defect”, remains an open question. Is this unwanted impurity already present in the germane gas used during diamond growth or lurking within the substrate itself?

Future work will focus on identifying the source of limited spin coherence to further refine these promising building blocks for future networks. This method avoids damage typically caused by ion implantation while achieving high concentrations of germanium atoms without introducing material stress, a vital step toward scalable devices. The team demonstrably created germanium-vacancy centres with unprecedented control and minimal material stress; reaching coherence times exceeding 730ns represents strong progress, even considering remaining questions about paramagnetic impurities.

This research successfully localized germanium-vacancy centers, promising components for quantum networking, within a ten nanometer layer of diamond during its growth using microwave plasma chemical vapor deposition. By carefully controlling the introduction of germanium, researchers achieved a sheet density of 0.12 GeV^-/μm² in an environment free from damaging strain, resulting in improved spectral resolution with linewidths averaging $47 pm 11$ MHz. The generated color centers exhibited spin coherence exceeding 730ns; however, identifying the source of this limit due to a paramagnetic defect remains an area for future study.

👉 More information
🗞 Delta-Doped GeV$^-$ in diamond with isotope resolvable optical spectra
✍️ Ian N. Hammock, Antoni W. Wellisz, Keira Linder, Jiefei Zhang, Xinghan Guo, Benjamin Pingault, David D. Awschalom, F. Joseph Heremans, Alexander A. High and Nazar Delegan (Pritzker School of Molecular Engineering, University of Chicago, Chicago, USA); Kinfung Ngan and Shuo Sun (JILA and Department of Physics, University of Colorado Boulder, Boulder, USA); Midrel Wilfried Ngandeu Ngambou (Materials Science Division and Center for Molecular Engineering, Argonne National Laboratory, Lemont, USA)
🧠 ArXiv: https://arxiv.org/abs/2610.30375

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