Electrostatic modulation of orbital energy splittings in a Ge/SiGe double quantum dot

Hole spin qubits in germanium quantum wells utilize orbital excited states for Pauli spin blockade readout. This allows them to avoid the challenges associated with low-lying excited valley states encountered by electrons in silicon quantum wells. Furthermore, orbital excited states, if tunable, could be used to encode a hole-based quantum dot hybrid qubit (QDHQ). It is important in both cases to understand the tunability of the orbital energy levels to maximize qubit control fidelity and to avoid leakage out of a qubit’s computational subspace. Here, we study the dependence of the orbital energy splittings in a double quantum dot formed in a Ge/SiGe heterostructure on the voltages applied to its proximal gates. By measuring the orbital energy splittings using photon-assisted tunneling and pulsed-gate spectroscopy, we show how the orbital energy splittings change throughout the region in gate-voltage space comprising the (2,1) and (1,2) charge configurations, where a hole-based QDHQ would be operated. We find that by adjusting the gate voltages that control the confinement of the quantum dots, we can tune the orbital splitting for the right quantum dot, E_Orb,R/h, in the range of 17-45 GHz and the orbital splitting for the left quantum dot, E_Orb,L/h, in the range of 78-96 GHz.