Direct measurement of a $\sin(2\varphi)$ current phase relation in a graphene superconducting quantum interference device

TL;DR

This paper reports the direct measurement of a $ ext{sin}(2 ext{phi})$ current phase relation in a graphene-based superconducting quantum interference device, revealing a harmonic that could enhance quantum bit protection.

Contribution

It demonstrates the first direct measurement of a $ ext{sin}(2 ext{phi})$ current phase relation in a graphene Josephson junction, showing a harmonic free of the usual $ ext{sin}( ext{phi})$ component.

Findings

Observation of $ ext{sin}(2 ext{phi})$ current phase relation.

Graphene Josephson junctions can exhibit non-standard phase relations.

Potential for improved superconducting qubits with reduced decoherence.

Abstract

In a Josephson junction, the current phase relation relates the phase variation of the superconducting order parameter, $\varphi$, between the two superconducting leads connected through a weak link, to the dissipationless current . This relation is the fingerprint of the junction. It is usually dominated by a $\sin(\varphi)$ harmonic, however its precise knowledge is necessary to design superconducting quantum circuits with tailored properties. Here, we directly measure the current phase relation of a superconducting quantum interference device made with gate-tunable graphene Josephson junctions and we show that it can behave as a $\sin(2\varphi)$ Josephson element, free of the traditionally dominant $\sin(\varphi)$ harmonic. Such element will be instrumental for the development of superconducting quantum bits protected from decoherence.