Quantum dot spectroscopy of proximity-induced superconductivity in a two-dimensional electron gas

We report the realization of a hybrid superconductor-quantum dot device by means of top-down nanofabrication starting from a two-dimensional electron gas in a InGaAs/InAlAs semiconductor heterostructure. The quantum dot is defined by electrostatic gates placed within the normal region of a planar Nb-InGaAs quantum well-Nb junction. Measurements in the regime of strong Coulomb blockade as well as cotunneling spectroscopy allow to directly probe the proximity-induced energy gap in a ballistic two-dimensional electron gas coupled to superconductors.