Superinductor-based ultrastrong coupling in a superconducting circuit

• URL: http://arxiv.org/abs/2507.09339v1
• Date: Sat, 12 Jul 2025 16:38:45 GMT
• Title: Superinductor-based ultrastrong coupling in a superconducting circuit
• Authors: Alba Torras-Coloma, Luca Cozzolino, Ariadna Gómez-del-Pulgar-Martínez, Elia Bertoldo, P. Forn-Díaz,
• Abstract summary: We present an ultrastrong superinductor-based coupling consisting of a flux qubit galvanically coupled to a resonator.<n>Our results show that superinductors are a promising tool to study USC physics in high-coherence circuits.
• Score: 0.0
• License: http://creativecommons.org/licenses/by/4.0/
• Abstract: We present an ultrastrong superinductor-based coupling consisting of a flux qubit galvanically coupled to a resonator. The coupling inductor is fabricated in granular Aluminum, a superinductor material able to provide large surface inductances. Spectroscopy measurements on the qubit-resonator system reveal a Bloch-Siegert shift of \SI{23}{\mega\hertz} and a coupling fraction of $g/\omega_r \simeq 0.13$, entering the perturbative ultrastrong coupling (USC) regime. We estimate the inductance of the coupler independently by low-temperature resistance measurements providing $L_c = (0.74\pm0.14)\,\mathrm{nH}$, which is compatible with $g/\omega \gtrsim 0.1$. Our results show that superinductors are a promising tool to study USC physics in high-coherence circuits using flux qubits with small loop areas and low persistent currents.

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