The hybrid Josephson rhombus: A superconducting element with tailored current-phase relation

TL;DR

The paper introduces a hybrid Josephson rhombus circuit with tunable current-phase relation, enabling control over superconducting properties for advanced quantum device applications.

Contribution

It presents a novel hybrid Josephson rhombus with magnetic and gate control, demonstrating tailored current-phase relations and diode effects for quantum technology.

Findings

Achieved $ ext{cos}(2 ext{phi})$ potential at full frustration.

Demonstrated superconducting diode effect with >25% efficiency.

Showcased tunability of the current-phase relation via magnetic and gate controls.

Abstract

Controlling the current-phase relation (CPR) of Josephson elements is essential for tailoring the eigenstates of superconducting qubits, tuning the properties of parametric amplifiers, and designing nonreciprocal superconducting devices. Here, we introduce the hybrid Josephson rhombus, a highly tunable superconducting circuit containing four semiconductor-superconductor hybrid Josephson junctions embedded in a loop. Combining magnetic frustration with gate-voltage-controlled tuning of individual Josephson couplings provides deterministic control of the harmonic content of the rhombus CPR. We show that for balanced Josephson couplings at full frustration, the hybrid rhombus displays a $\pi$-periodic $\cos(2\varphi)$ potential, indicating coherent charge-$4e$ transport. Tuning away from the balanced configuration, we observe a superconducting diode effect with efficiency exceeding 25%. These results showcase the potential of hybrid Josephson rhombi as fundamental building blocks for noise-resilient qubits and quantum devices with custom transport properties.