Superinductor-based ultrastrong coupling in a superconducting circuit
We present an ultrastrong superinductor-based coupling mechanism in a circuit consisting of a flux qubit galvanically coupled to an LC resonator. The coupling inductor is fabricated with granular aluminum, a superinductor material able to provide large surface inductances. Despite the low persistent current exhibited by the qubit, Ip=11.6 nA, spectroscopy measurements reveal a Bloch–Siegert shift of 23 MHz and a coupling fraction of g/ωr≃0.13, entering the perturbative ultrastrong coupling regime. An independent estimate of the coupler inductance by low-temperature resistance measurements leads to Lc=(0.74±0.14) nH, which is compatible with g/ωr≳0.1. Our results show that superinductors are a promising resource to study ultrastrong coupling physics in high-coherence circuits using flux qubits with small loop areas and low persistent currents.
Authors
- E. Bertoldo (ORCID: https://orcid.org/0000-0001-6260-0325)
- Luis D. Cozzolino (ORCID: https://orcid.org/0000-0002-0548-373X)
- P. Forn-Díaz (ORCID: https://orcid.org/0000-0003-4365-5157)
- Alba Torras-Coloma (ORCID: https://orcid.org/0000-0002-9847-8170)
- Ariadna Gómez-del-Pulgar-Martínez (ORCID: https://orcid.org/0009-0002-9493-2329)
Institutions
- Universitat Autònoma de Barcelona (ES)
- Institute for High Energy Physics (ES)
- Barcelona Supercomputing Center (ES)
- Quantum Devices (United States) (US)
- Universitat de Barcelona (ES)
- Universitat Politècnica de Catalunya (ES)
Publication Details
- Journal
- Applied Physics Letters
- Published
- 2025-11-24
- DOI
- https://doi.org/10.1063/5.0293790
- Citations
- 1
- Primary Topic
- Mechanical and Optical Resonators
- Type
- article
- Field-Weighted Citation Impact
- 1.25
Funders
- Centres de Recerca de Catalunya
- European Commission
- Generalitat de Catalunya
- Ministerio de Economía y Competitividad
- QuantERA
- Institut de Física d'Altes Energies
- Agència de Gestió d'Ajuts Universitaris i de Recerca