Strong charge-photon coupling in planar germanium enabled by granular aluminium superinductors
High kinetic inductance superconductors are gaining increasing interest for the realisation of qubits, amplifiers and detectors. Moreover, thanks to their high impedance, quantum buses made of such materials enable large zero-point fluctuations of the voltage, boosting the coupling rates to spin and charge qubits. However, fully exploiting the potential of disordered or granular superconductors is challenging, as their inductance and, therefore, impedance at high values are difficult to control. Here, we report a reproducible fabrication of granular aluminium resonators by developing a wireless ohmmeter, which allows in situ measurements during film deposition and, therefore, control of the kinetic inductance of granular aluminium films. Reproducible fabrication of circuits with impedances (inductances) exceeding 13 kΩ (1 nH per square) is now possible. By integrating a 7.9 kΩ resonator with a germanium double quantum dot, we demonstrate strong charge-photon coupling with a rate of g<sub>c</sub>/2π = 566 ± 2 MHz. This broadly applicable method opens the path for novel qubits and high-fidelity, long-distance two-qubit gates.
Authors
- Stefano Calcaterra (ORCID: https://orcid.org/0009-0001-7543-8360)
- Georgios Katsaros (ORCID: https://orcid.org/0000-0001-8342-202X)
- Jordi Arbiol (ORCID: https://orcid.org/0000-0002-0695-1726)
- Kévin Roux (ORCID: https://orcid.org/0000-0003-4832-7726)
- Daniel Chrastina (ORCID: https://orcid.org/0000-0002-1054-3717)
- Marc Botifoll (ORCID: https://orcid.org/0000-0002-4876-6393)
- Alba Garzón Manjón (ORCID: https://orcid.org/0000-0003-2954-1102)
- Carla Borja-Espinosa
- Olivér Sági
- Giovanni Isella (ORCID: https://orcid.org/0000-0001-5951-7440)
- Ioan M. Pop (ORCID: https://orcid.org/0000-0002-6776-9792)
- Abdulhamid Baghdadi
- Thomas Adletzberger
- Marián Janík
Institutions
- University of Stuttgart (DE)
- Karlsruhe Institute of Technology (DE)
- Institució Catalana de Recerca i Estudis Avançats (ES)
- Institute of Chemistry of the Slovak Academy of Sciences (SK)
- Institute of Science and Technology Austria (AT)
- Slovak Academy of Sciences (SK)
- Institut Català de Nanociència i Nanotecnologia (ES)
- Institute of Electrical Engineering of the Slovak Academy of Sciences (SK)
- Politecnico di Milano (IT)
Publication Details
- Journal
- Nature Communications
- Published
- 2025-03-01
- DOI
- https://doi.org/10.1038/s41467-025-57252-4
- Citations
- 11
- Primary Topic
- Quantum and electron transport phenomena
- Type
- article
- Field-Weighted Citation Impact
- 13.71
Funders
- Institute of Science and Technology Austria
- European Commission
- Deutsche Forschungsgemeinschaft
- Austrian Science Fund
- NOMIS Stiftung