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.