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

In a Josephson junction, the current phase relation relates the phase variation of the superconducting order parameter, $φ$, 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 $\sin(φ)$ 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 $\sin(2φ)$ Josephson element, free of the traditionally dominant $\sin(φ)$ harmonic. Such element will be instrumental for the development of superconducting quantum bits protected from decoherence.