Josephson φ0-junction in nanowire quantum dots

The Josephson effect describes supercurrent flowing through a junction connecting two superconducting leads by a thin barrier(1). This current is driven by a superconducting phase difference phi between the leads. In the presence of chiral and time-reversal symmetry of the Cooper pair tunnelling process(2), the current is strictly zero when phi vanishes. Only if these underlying symmetries are broken can the supercurrent for phi = 0 be finite(3-5). This corresponds to a ground state of the junction being offset by a phase phi(0), different from 0 or pi. Here, we report such a Josephson phi(0)-junction based on a nanowire quantum dot. We use a quantum interferometer device to investigate phase offsets and demonstrate that phi(0) can be controlled by electrostatic gating. Our results may have far-reaching implications for superconducting flux-and phase-defined quantum bits as well as for exploring topological superconductivity in quantum dot systems.