Supercurrent through an Andreev trimer

Supercurrent through quantum dots embedded into hybrid superconductor–semiconductor–superconductor Josephson junctions has been widely investigated in the last two decades. However, previous studies were blind to the physics taking place below each superconducting lead. Here we realize a device with additional normal-metal tunneling probes, unveiling the Andreev bound states (ABSs) populating the spectrum underneath each superconductor. Such ABSs play a crucial role, that is essential for matching theory and experimental data. Furthermore, by varying the ABS chemical potentials with electrostatic gates, we show how to control the supercurrent through the quantum dot and, in particular, increase its maximum by up to two orders of magnitude. Finally, we show how a strong coupling between the ABSs and the quantum dot can create a three-site Andreev molecule.