article published yes Jaime Saez Mollejo author e0390f72-f6e0-11ea-865d-862393336714 Daniel Jirovec author 4C473F58-F248-11E8-B48F-1D18A9856A870000-0002-7197-4801 Yona A Schell author fe39122d-06bb-11ec-a33b-9e22b40e40a5 Josip Kukucka author 3F5D8856-F248-11E8-B48F-1D18A9856A87 Stefano Calcaterra author Daniel Chrastina author Giovanni Isella author Maximilian Rimbach-Russ author Stefano Bosco author Georgios Katsaros author 38DB5788-F248-11E8-B48F-1D18A9856A870000-0001-8342-202X GeKa department Integrated Germanium Quantum Technology project Center for Correlated Quantum Materials and Solid State Quantum Systems: Conventional and unconventional topological superconductors project High impedance circuit quantum electrodynamics with hole spins project Hybrid Semiconductor - Superconductor Quantum Devices project FWF Open Access Fund project Hole spin qubits are rapidly emerging as the workhorse of semiconducting quantum processors because of their large spin-orbit interaction, enabling fast all-electric operations at low power. However, spin-orbit interaction also causes non-uniformities in devices, resulting in locally varying qubit energies and site-dependent anisotropies. While these anisotropies can be used to drive single-spins, if not properly harnessed, they can hinder the path toward large-scale quantum processors. Here, we report on microwave-driven singlet-triplet qubits in planar germanium and use them to investigate the anisotropy of two spins in a double quantum dot. We show two distinct operating regimes depending on the magnetic field direction. For in-plane fields, the two spins are largely anisotropic, and electrically tunable, which enables to measure all the available transitions; coherence times exceeding 3 $\mu$s are extracted. For out-of-plane fields, they have an isotropic response but preserve the substantial energy difference required to address the singlet-triplet qubit. Even in this field direction, where the qubit lifetime is strongly affected by nuclear spins, we find 400 ns coherence times. Our work adds a valuable tool to investigate and harness the anisotropy of spin qubits and can be implemented in any large-scale NxN device, facilitating the path towards scalable quantum processors. https://research-explorer.ista.ac.at/download/19424/19645/2025_NatureComm_SaezMollejo.pdf application/pdfno Springer Nature2025 eng 2041-1723 2408.03224 40274808 00147558740002210.1038/s41467-025-58969-y 16 https://research-explorer.ista.ac.at/record/19409 https://research-explorer.ista.ac.at/record/19836 https://ista.ac.at/en/news/the-shadow-of-an-electron/ Saez Mollejo J, Jirovec D, Schell YA, Kukucka J, Calcaterra S, Chrastina D, Isella G, Rimbach-Russ M, Bosco S, Katsaros G. 2025. Exchange anisotropies in microwave-driven singlet-triplet qubits. Nature Communications. 16, 3862. Saez Mollejo, Jaime, Daniel Jirovec, Yona A Schell, Josip Kukucka, Stefano Calcaterra, Daniel Chrastina, Giovanni Isella, Maximilian Rimbach-Russ, Stefano Bosco, and Georgios Katsaros. “Exchange Anisotropies in Microwave-Driven Singlet-Triplet Qubits.” <i>Nature Communications</i>. Springer Nature, 2025. <a href="https://doi.org/10.1038/s41467-025-58969-y">https://doi.org/10.1038/s41467-025-58969-y</a>. Saez Mollejo J, Jirovec D, Schell YA, et al. Exchange anisotropies in microwave-driven singlet-triplet qubits. <i>Nature Communications</i>. 2025;16. doi:<a href="https://doi.org/10.1038/s41467-025-58969-y">10.1038/s41467-025-58969-y</a> Saez Mollejo, J., Jirovec, D., Schell, Y. A., Kukucka, J., Calcaterra, S., Chrastina, D., … Katsaros, G. (2025). Exchange anisotropies in microwave-driven singlet-triplet qubits. <i>Nature Communications</i>. Springer Nature. <a href="https://doi.org/10.1038/s41467-025-58969-y">https://doi.org/10.1038/s41467-025-58969-y</a> Saez Mollejo, Jaime, et al. “Exchange Anisotropies in Microwave-Driven Singlet-Triplet Qubits.” <i>Nature Communications</i>, vol. 16, 3862, Springer Nature, 2025, doi:<a href="https://doi.org/10.1038/s41467-025-58969-y">10.1038/s41467-025-58969-y</a>. J. Saez Mollejo, D. Jirovec, Y.A. Schell, J. Kukucka, S. Calcaterra, D. Chrastina, G. Isella, M. Rimbach-Russ, S. Bosco, G. Katsaros, Nature Communications 16 (2025). J. Saez Mollejo <i>et al.</i>, “Exchange anisotropies in microwave-driven singlet-triplet qubits,” <i>Nature Communications</i>, vol. 16. Springer Nature, 2025. 194242025-03-19T13:28:12Z2026-07-11T22:30:33Z