RAMPAGE · Realization and Manipulation of a Planar hybrid superconducting Andreev spin qubit in GErmanium

In the boiling field of quantum technology, the development of a stable, inherently shielded from perturbations quantum register is essential, yet remains elusive. Hybrid semiconductor-superconductor devices have been intensively studied, hunting for Majorana bound states towards topological quantum computing. While this goal has not yet been achieved, it has spurred material developments in III-V semiconductors, creating a new playground for spin qubits, resulting from the hybridization of the semiconductor and the superconductor in 1D Josephson junctions. Pioneering experiments recently demonstrated the manipulation of such a hybrid qubit, the Andreev spin qubit (ASQ), highlighting the potential of this approach. However, it is now reaching its limits due to the intrinsic properties of the host III-V semiconductor and the nanowire geometry, calling for a more suitable platform not demonstrated to date. In this proposal, I will tackle this challenge by fabricating a hybrid electrostatically tunable 1D Josephson junctions from a 2D germanium heterostructure. The first realization of a 1D Josephson weak ling on a planar Ge heterostructure will experimentally prove the possible integration of hybrid junctions, with resolved Andreev bound states. This device will enable the study of the spin-orbit interaction Hamiltonian for holes in 1D, a topic that remains largely unexplored leveraging microwave spectroscopy of Andreev bound states. Then, harnessing the unique properties of Ge, I will realize the first ASQ on a group IV semiconductor heterostructure. The proposed hybrid superconducting ASQ sets a significant milestone in the field, paving the way towards larger ensembles and enabling straightforward microwave connectivity using standard circuit quantum electrodynamic techniques. This harmoniously blends the benefits of semiconductor spin qubits with superconducting circuits, offering a promising path toward topologically protected qubits.