We investigate the ultrastrong tunable coupler for coupling of superconducting resonators. Obtained coupling constant exceeds 1 GHz, and the wide range tunability is achieved both antiferromagnetics and ferromagnetics from −1086 MHz to 604 MHz. The ultrastrong coupler is composed of rf-SQUID and dc-SQUID as tunable junctions, which connected to resonators via shared aluminum thin film meander lines enabling such a huge coupling constant. The spectrum of the coupler obviously shows the breaking of the rotating wave approximation, and our circuit model treating the Josephson junction as a tunable inductance reproduces the experimental results well. The ultrastrong coupler is expected to be utilized in quantum annealing circuits and/or NISQ devices with dense connections between qubits.
@article{arxiv.2107.13175,
title = {Ultrastrong tunable coupler between superconducting LC resonators},
author = {Takafumi Miyanaga and Akiyoshi Tomonaga and Hikaru Ito and Hiroto Mukai and Jaw-Shen Tsai},
journal= {arXiv preprint arXiv:2107.13175},
year = {2023}
}