A quantum dot in germanium proximitized by a superconductor
Abstract: Planar germanium quantum wells have recently been shown to host hard-gapped superconductivity. Additionally, quantum dot spin qubits in germanium are well-suited for quantum information processing, with isotopic purification to a nuclear spin-free material expected to yield long coherence times. Therefore, as one of the few group IV materials with the potential to host superconductor-semiconductor hybrid devices, proximitized quantum dots in germanium is a compelling platform to achieve and combine topological superconductivity with existing and novel qubit modalities. Here we demonstrate a quantum dot (QD) in a Ge/SiGe heterostructure proximitized by a platinum germanosilicide (PtGeSi) superconducting lead (SC), forming a SC-QD-SC junction. We show tunability of the QD-SC coupling strength, as well as gate control of the ratio of charging energy and the induced gap. We further exploit this tunability by exhibiting control of the ground state of the system between even and odd parity. Furthermore, we characterize the critical magnetic field strengths, finding a critical out-of-plane field of 0.90(4). Finally we explore sub-gap spin splitting in the device, observing rich physics in the resulting spectra, that we model using a zero-bandwidth model in the Yu-Shiba-Rusinov limit. The demonstration of controllable proximitization at the nanoscale of a germanium quantum dot opens up the physics of novel spin and superconducting qubits, and Josephson junction arrays in a group IV material.
- M. Leijnse and K. Flensberg, Parity qubits and poor man’s majorana bound states in double quantum dots, Phys. Rev. B 86, 134528 (2012).
- A. Y. Kitaev, Unpaired majorana fermions in quantum wires, Physics-Uspekhi 44, 10.1070/1063-7869/44/10S/S29 (2001).
- D. M. Pino, R. S. Souto, and R. Aguado, Minimal kitaev-transmon qubit based on double quantum dots, Phys. Rev. B 109, 075101 (2024).
- T. Nishimura, K. Kita, and A. Toriumi, Evidence for strong Fermi-level pinning due to metal-induced gap states at metal/germanium interface, Applied Physics Letters 91, 123123 (2007).
- M. Valentini, O. Sagi, and L. e. a. Baghumyan, Parity-conserving cooper-pair transport and ideal superconducting diode in planar germanium, Nat Commun 15, 10.1038/s41467-023-44114-0 (2024).
- E. Zhuo, Z. Lyu, and X. S. et al., Hole-type superconducting gatemon qubit based on ge/si core/shell nanowires, npj quantum information 9, 10.1038/s41534-023-00721-9 (2023).
- M. Leijnse and K. Flensberg, Coupling spin qubits via superconductors, Phys. Rev. Lett. 111, 060501 (2013).
- J. Bauer, A. Oguri, and A. C. Hewson, Spectral properties of locally correlated electrons in a bardeen–cooper–schrieffer superconductor, Journal of Physics: Condensed Matter 19, 486211 (2007).
- T. Meng, S. Florens, and P. Simon, Self-consistent description of andreev bound states in josephson quantum dot devices, Physical Review B 79, 224521 (2009a).
- T. Meng, S. Florens, and P. Simon, Self-consistent description of andreev bound states in josephson quantum dot devices, Phys. Rev. B 79, 224521 (2009b).
- E. Lee, X. Jiang, and M. e. a. Houzet, Spin-resolved andreev levels and parity crossings in hybrid superconductor–semiconductor nanostructures, Nature Nanotechnology 9, 79–84 (2014).
- L. Yu, Bound states in paramagnetic impurity-containing superconductors, Chinese Jounral of Physics 21, 21 (1965).
- H. Shiba, Classical Spins in Superconductors, Progress of Theoretical Physics 40, 435 (1968).
- A. I. Rusinov, Superconcductivity near a Paramagnetic Impurity, Letters to JETP 9, 146 (1969).
- V. V. Baran, E. J. Frost, and J. Paaske, Surrogate model solver for impurity-induced superconducting subgap states, Physical Review B 108, L220506 (2023).
- M. Tinkham, Introduction to Superconductivity, 2nd ed. (Dover Publications, 2004).
- P. Fulde, High field superconductivity in thin films, Advances in Physics 22, 667 (1973).
- N. Hendrickx, D. Franke, and A. e. a. Sammak, Fast two-qubit logic with holes in germanium, Nature , 487–491 (2020a).
- N. Hendrickx, D. Franke, and A. e. a. Sammak, A single-hole spin qubit, Nature Communications (2020b).
- P. Chandra, P. Coleman, and R. Flint, Hastatic order in the heavy-fermion compound uru2si2, Nature 493, 621 (2013).
- K. Laubscher, J. D. Sau, and S. Das Sarma, Germanium-based hybrid semiconductor-superconductor topological quantum computing platforms: Disorder effects, arXiv preprint arXiv:2404.16285 (2024).
Paper Prompts
Sign up for free to create and run prompts on this paper using GPT-5.
Top Community Prompts
Collections
Sign up for free to add this paper to one or more collections.