Flux-Tunable Josephson Diode Effect in a Hybrid Four-Terminal Josephson Junction

We investigate the direction-dependent switching current in a flux-tunable four-terminal Josephson junction defined in an InAs/Al two-dimensional heterostructure. The device exhibits the Josephson diode effect, with switching currents that depend on the sign of the bias current. The superconducting diode efficiency, reaching a maximum of $|\eta|\approx34\%$, is widely tunable - both in amplitude and sign - as a function of magnetic fluxes and gate voltages. Our observations are supported by a circuit model of three parallel Josephson junctions with non-sinusoidal current-phase relation. With respect to conventional Josephson interferometers, phase-tunable multiterminal Josephson junctions enable large diode efficiencies in structurally symmetric devices, where local magnetic fluxes break both time-reversal and spatial-inversion symmetries. Our work establishes a pathway to develop Josephson diodes with wide-range tunability and that do not rely on exotic materials or externally applied magnetic fields.