Three-Josephson junctions flux qubit couplings

We analyze the coupling of two flux qubits with a general many-body projector into the low-energy subspace. Specifically, we extract the effective Hamiltonians that controls the dynamics of two qubits when they are coupled via a capacitor and/or via a Josephson junction. While the capacitor induces a static charge coupling tunable by design, the Josephson junction produces a magnetic-like interaction easily tunable by replacing the junction with a superconducting quantum interference device. Those two elements allow to engineer qubits Hamiltonians with XX, YY, and ZZ interactions, including ultrastrongly coupled ones. We present an exhaustive numerical study for two three-Josephson junctions flux qubit that can be directly used in experimental work. The method developed here, namely, the numerical tool to extract qubit effective Hamiltonians at strong coupling, can be applied to replicate our analysis for general systems of many qubits and any type of coupling.

Automated summary

This study investigates the coupling of two flux qubits through a capacitor and Josephson junction, extracting effective Hamiltonians for controlling qubit dynamics. By tuning static charge coupling with capacitors and magnetic-like interactions with Josephson junctions, various qubit Hamiltonians with different interactions can be engineered, including ultrastrongly coupled ones. An exhaustive numerical study on a three-Josephson junctions flux qubit is presented, which can be directly applied in experimental work, and the developed numerical tool can be used to analyze general systems of many qubits and any type of coupling.