Coupling of quantum dots with superconductors - towards long-range coupling of qubits
Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering
Final Report Abstract
Achieving long-range coupling of qubits would be a major milestone paving the way for upscaling quantum information processors based on semiconducting spin qubits. The current project aimed at laying the foundation for realizing this long-range coupling via superconductors. Two different approaches were pursued. The first approach used InAs nanowires with in-situ deposition of a well-defined insulating barrier and superconductor in order to access the full-range of coupling strengths between super- and semiconductor. The second approach was based on superconductor-silicon junctions. While this leads to a limited range of coupling strengths the benefit is that immediate coupling to spin qubits (e.g. in 28Si) becomes feasible, facilitating a true upscaling of the numbers of qubits. The latter approach used self-aligned CoSi2 with dopant segregation and ultrathin SiN depinning layers in order to tune the coupling strength. While the final project goal could not yet be achieved, the project will be continued on the participants own resources. Nevertheless, parts of the developed processes led to important insights and further research that has been published in appropriate scientific journals. The results of the project are the following: Within the project Te has been demonstrated to provide n-type doping for InAs. InAs nanowires have been covered in-situ with Al2O3 and a superconducting Al half-shell and the influence of the oxide thickness on the electric transport has been investigated. In addition, a damascene process for the realization of bottom gate structures has been developed in order to electrostatically define quantum dots in InAs nanowires with Al half-shell. Devices based on two different types of bottom gates have been fabricated and characterised at room temperature. Two types of superconductor-silicon junctions based on CoSi2 with dopant segregation and with ultrathin SiN interface layer were realized and are currently measured or will be in the near future. The CoSi2 approach facilitates a self-aligned process by transferring silicon patterns into a superconductor with silicidation. Furthermore, dopant segregation can be employed to modify the barrier between super- and semiconductor. The second approach is based on anisotropic silicon etching and a damascene process allows the creating of very short SNS junctions (24nm and below in the present case) without any nanolithography. The combination with a Fermi level depinning, ultrathin SiN layer allows tuning the coupling between super- and semiconductor. The methods and processing techniques developed within the project were further developed and published in appropriate scientific journals.
Publications
- ‘‘Spin qubits confined to a silicon nano-ridge’’, Appl. Sci., 9, 3823 (2019)
J. Klos, B. Sun, J. Beyer, S. Kindel, L. Hellmich, J. Knoch, L. Schreiber
(See online at https://doi.org/10.3390/app9183823) - ‘Role of electron and ion irradiation in a reliable lift-off process with electron beam evaporation and a bilayer PMMA resist system’’, J. Vac. Sci. Technol. B, 39(5), 052601 (2021)
B. Sun, T. Grap, T. Frahm, S. Scholz and J. Knoch
(See online at https://doi.org/10.1116/6.0001161) - ‘‘Modeling and prediction of hydrogen-assisted morphological evolution in silicon utilizing a level-set approach’’, IEEE J. Microelectromech. Sys., 30(6), 950-957 (2021)
B. Sun, S. Scholz, A. Kemper, T. Grap and J. Knoch
(See online at https://doi.org/10.1109/JMEMS.2021.3115715) - ‘‘On the Operation Modes of Dual-Gate Reconfigurable Nanowire Transistors’’, IEEE Trans. Electron Dev., 68(7), 3684-3689 (2021)
B. Sun, B. Richstein, P. Liebisch, T. Frahm, S. Scholz, J. Trommer, T. Mikolajick and J. Knoch
(See online at https://doi.org/10.1109/TED.2021.3081527) - „Electrical Characterization of Te-doped InAs Nanowires grown by Vapor-Solid Molecular Beam Epitaxy“, Conference Contribution (DPG Jahrestagung, online) (2021)
A. Faustmann, P. Perla, D. Grützmacher, M. I. Lepsa, and T. Schäpers
- „Te-doped selective-area grown InAs nanowires for superconducting hybrid devices“, Phys. Rev. Materials 6, 024602 (2022)
P. Perla, A. Faustmann, S. Kölling, P. Zellekens, R. Deacon, H. A. Fonseka, J. Kölzer, Y. Sato, A. M. Sanchez, O. Moutanabbir, K. Ishibashi, D. Grützmacher, M. I. Lepsa, and T. Schäpers
(See online at https://doi.org/10.1103/PhysRevMaterials.6.024602)
