Phys. Rev. A 107, 012434 (2023)

Spin-wave-based tunable coupler between superconducting flux qubits

Shaojie Yuan^1,2, Chuanpu Liu³, Jilei Chen¹, Song Liu¹, Jin Lan⁴, Haiming Yu³, Jiansheng Wu¹, Fei Yan¹, Man-Hong Yung¹, Jiang Xiao⁵, Liang Jiang⁶ and Dapeng Yu¹

1 Institute for Quantum Science and Engineering, and Department of Physics, Southern University of Science and Technology, Shenzhen 518055, China

2 Department of Physics, Yancheng Institute of Technology, Yancheng 224051, People’s Republic of China

3 Fert Beijing Research Institute, School of Electronic and Information Engineering, BDBC, Beihang University, 100191 Beijing, China

4 Center of Joint Quantum Studies and Department of Physics, School of Science, Tianjin University, Tianjin 300350, China

5 Department of Physics and State Key Laboratory of Surface Physics, Fudan University, Shanghai 200433, China

6 Pritzker School of Molecular Engineering, The University of Chicago, Chicago, Illinois 60637, USA

Abstract

Quantum computing and simulation based on superconducting qubits have achieved significant progress and entered the noisy intermediate-scale quantum (NISQ) era recently. Using a third qubit or object as a tunable coupler between qubits is an important step in this process. In this article, we propose a hybrid system made of superconducting qubit and a yttrium iron garnet (YIG) system as an alternative way to realize this. YIG thin films have spin wave (magnon) modes with low dissipation and reliable control for quantum information processing. Here, we propose a scheme to achieve strong coherent coupling between superconducting (SC) flux qubits and magnon modes in YIG thin film. Unlike the direct $\sqrt{N}$ enhancement factor in coupling to the Kittel mode and other spin ensembles, with $N$ the total number of spins, an additional spatial-dependent phase factor needs to be considered when the qubits are magnetically coupled with the magnon modes of finite wavelength. To avoid undesirable cancellation of coupling caused by the symmetrical boundary condition, a CoFeB thin layer is added to one side of the YIG thin film to break the symmetry. Our numerical simulation demonstrates avoided crossing and coherent transfer of quantum information between the flux qubit and the standing spin waves in YIG thin films. We show that the YIG thin film can be used as a tunable coupler between two flux qubits, which have a modified shape with small direct inductive coupling between them. Our results manifest that by cancellation of direct inductive coupling and indirect spin-wave couple of flux qubits we can turn on and off the net coupling between qubits. This bring magnonic YIG thin film into the field of quantum information processing.