Pearl-Vortex Tunneling in Magic-Angle Twisted Graphene.

Twisted graphene provides a tunable platform for studying superconductivity in two dimensions. In the presence of electric currents and magnetic fields, vortices determine the phenomenological properties of the material. Here, we employ a gate-defined Josephson junction as a single-vortex sensor, enabling direct access to individual vortex dynamical events. Our measurements reveal that vortices enter the superconducting leads via classical thermal activation over energy barriers at elevated temperatures T>100  mK. At low temperatures T<90  mK, we observe macroscopic quantum tunneling through these barriers. The data are consistent with a sharp, first-order type quantum-to-classical transition. From our measurements, we extract vortex entry and exit energy barriers on the order of a few kelvins and estimate the barrier thickness to be approximately 100 nm.