A Kapitza Pendulum Route to Supercurrent Tunnel Diodes

Superconducting diodes that support nonreciprocal supercurrent flow in principle constitute attractive, non-dissipative, circuit elements for superconducting electronics. But their realization faces fundamental challenges, as conventional Josephson tunnel junctions are inherently reciprocal. Existing approaches to break reciprocity typically involve magnetism or spin-orbit coupling, which often increase device complexity and limit reproducibility. Here, we demonstrate an alternative dynamical route to supercurrent nonreciprocity based on parametric driving. By applying a frequency-modulated supercurrent amplitude we show that effective higher-order, nonharmonic terms are generated in the current-phase relation. Leveraging mathematical equivalences with the Kapitza pendulum, we show that these terms dynamically break reciprocity. This establishes the concept of a Kapitza supercurrent diode and demonstrates that nonreciprocal superconducting transport can be engineered by nonequilibrium driving conventional Josephson tunnel junctions. We propose two implementations of the Kapitza supercurrent diode - via gate-controlled superconducting interferometers or flux-driven double-loop SQUIDs - to achieve nonreciprocal supercurrent transport within experimentally accessible frequencies $\omega/2\pi \sim 1$-$10\,\mathrm{GHz}$.