Dresden 2026 – scientific programme

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QI: Fachverband Quanteninformation

QI 6: Implementations II

QI 6.5: Talk

Tuesday, March 10, 2026, 10:45–11:00, BEY/0245

Ge-based qubit heterostructure: A 3-in-1 photoelectron spectroscopy study — •Andreas Fuhrberg¹, Maximilian Oezkent², Kevin-P. Gradwohl², Sergii Chernov⁴, Volkmar Koller⁴, Christoph Schlueter⁴, Hans-Joachim Elmers³, and Martina Müller¹ — ¹Universität Konstanz — ²IKZ, Berlin — ³Universität Mainz — ⁴DESY, Hamburg

Semiconductor spin qubits are a key component in quantum information processing. Ge-based hole spin qubits have also proven to be a suitable system for realizing spin qubits. Strain-induced Ge_0.8Si_0.2/Ge/Ge_0.8Si_0.2 heterostructures are a common way to build such components. At both interfaces, holes are confined by a strain-induced valence band offset (VBO) - an essential device parameter.
A set of three synchrotron-based photoemission experiments are performed to investigate the interfaces of Ge-based qubit heterostructures by varying the thickness of (i) the central Ge-layer and (ii) Ge_0.8Si_0.2 overlayer. Using hard X-ray momentum microscopy (MM), the valence band along the symmetry points Γ, X and L is characterized, and the VBO near both interfaces is quantized. MM reveals an increased energy shift of ≈ 50 meV between the heavy/light hole band and the spin-orbit band for (i) Ge and (ii) Ge_0.8Si_0.2 bands near the respective interface. An MM-based diffraction experiments and hard X-ray photoelectron spectroscopy further analyse the interface structure and chemistry. Together, this three-in-one photoelectron spectroscopy technique provides a nearly full characterization of the Ge-hole spin qubits main structure and supports the qubit optimization process.

Keywords: Ge-Qubits; GeSi; Valence band; X-ray momentum microscopy