Work

Superinductor-based ultrastrong coupling in a superconducting circuit

Year: 2025

Type: article

Abstract: 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.

Source: Applied Physics Letters

DOI: 10.1063/5.0293790

Authors: Alba Torras-Coloma, Luca Cozzolino, Ariadna Gómez-del-Pulgar-Martínez, Elia Bertoldo, P. Forn-Díaz