Exchange anisotropies in microwave-driven singlet-triplet qubits Saez Mollejo, Jaime Jirovec, Daniel ; https://orcid.org/0000-0002-7197-4801 Schell, Yona A Kukucka, Josip Calcaterra, Stefano Chrastina, Daniel Isella, Giovanni Rimbach-Russ, Maximilian Bosco, Stefano Katsaros, Georgios ; https://orcid.org/0000-0001-8342-202X ddc:530 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. Springer Nature 2025 info:eu-repo/semantics/article doc-type:article text http://purl.org/coar/resource_type/c_2df8fbb1 https://research-explorer.ista.ac.at/record/19424 https://research-explorer.ista.ac.at/download/19424/19645 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> eng info:eu-repo/semantics/altIdentifier/doi/10.1038/s41467-025-58969-y info:eu-repo/semantics/altIdentifier/e-issn/2041-1723 info:eu-repo/semantics/altIdentifier/wos/001475587400022 info:eu-repo/semantics/altIdentifier/arxiv/2408.03224 info:eu-repo/semantics/altIdentifier/pmid/40274808 info:eu-repo/semantics/openAccess