Hole spin qubits in strained planar germanium quantum wells (Ge/SiGe) [1] have emerged as a promising qubit candidate for quantum information processing and simulation evidenced by the demonstration of single qubit fidelities above 99.99% [2], tune-up of a 4x4 quantum dot array [3] and the execution of multi-qubit quantum logic [4]. Recently, hard-gapped superconductivity has been engineered for the first time in Ge/SiGe, in a wide range of mesoscopic devices [5]. The demonstration of an isotopically purifiable semiconductor platform that can host clean superconductivity places Ge/SiGe in a uniquely advantageous position, facilitating many opportunities for hybrid superconducting-semiconducting quantum dots, including high fidelity two-qubit gates [6], extended range qubit-qubit coupling without the need for resonators [7], and integration with circuit QED [8]. In this work we make initial steps toward these goals, by presenting a proximiti zed germanium quantum dot (QD) coupled to a superconducting lead (S). We show the emergence of a superconducting gap within the charging energy of a quantum dot via bias spectroscopy, with tunable S-QD coupling. We use this to demonstrate switching between singlet and doublet ground states. We further characterize critical magnetic field strength, finding remarkably robust critical field strength of 0.911 T along the out-of-plane axis. Finally, we study spin splitting of sub-gab states, finding an out-of-plane g-factor of 6.11, and a large anisotropy of the g-factor for in- and out-of-plane field orientations. These results constitute a promising first step towards hybrid superconducting-semiconducting quantum information processing with hole spin qubit in Ge/SiGe.
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Publication:[1] G. Scappucci et al., Nat. Mat. Rev. (2022) [2] W.I.L Lawrie et al., Nat. Commun. (2023) [3] F. Borsoi et al., Nat. Nano. (2023) [4] N.W. Hendrickx et al., Nature. (2022) [5] A. Tosato et al., Comms. Mat. (2023) [6] M. Spethmann et al., ArXiv. (2023) [7] M. Leijnse et al., PRL. (2013) [8] M. Pita-Vidal et al., Nat. Phys. (2023)
Presenters
William Iain L Lawrie
QuTech and Kavli Institute of Nanoscience, Delft University of Technology, University of Copenhagen
Authors
William Iain L Lawrie
QuTech and Kavli Institute of Nanoscience, Delft University of Technology, University of Copenhagen
Lazar Lakic
Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen
David van Driel
Delft University of Technology
Lucas Stehouwer
QuTech and Kavli Institute of Nanoscience, Delft University of Technology
Menno Veldhorst
QuTech and Kavli Institute of Nanoscience, Delft University of Technology, Delft University of Technology
Giordano Scappucci
TU Delft QuTech, QuTech and Kavli Institute of Nanoscience, Delft University of Technology, TU Delft, QuTech and Kavli Institute of Nanoscience, TU Delft, The Netherlands
