A Kapitza Pendulum Route to Supercurrent Tunnel Diodes

Abstract

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 $ω/2π\sim 1$-$10\,\mathrm{GHz}$.

Figures (3)

• Figure 1: Current–voltage characteristics of a parametrically driven Josephson junction with anomalous phase $\phi=\pi/2$ at $i_\text{dc}=0$ for $i_\text{ac}=0.25$, $0.5$ ($\omega/\omega_{p0}=5$, black/blue), and $i_\text{ac}=2.25$, $20$ ($\omega/\omega_{p0}=50$, green/red). Inset: diode efficiency $\eta$ extracted from each curve. Filled markers indicate $I_c^{\pm}$, and color-matched dotted lines guide the eye. Damping $\beta/\omega_{p0}=0.1$, $i_{c,t}=2$.
• Figure 2: (a, c) Critical currents $I_c^{\pm}$ and (b, d) diode rectification $\eta$ of a driven Josephson junction versus $\omega/\omega_{p0}$ for $\phi=\pi/2$ (a, b) and $\phi=\pi/3$ (c, d) with $i_\text{dc}=0$, $i_\text{ac}=0.25$. Magenta dotted lines show high-frequency asymptotics from the weak-amplitude expansion (see main text).
• Figure 3: Schematic implementations of the Kapitza supercurrent diode using superconducting interferometers. (a) Gate-controlled SQUID, with time-dependent gate modulation (V$_g$) and a static flux ($\Phi$) -induced phase shift. (b) Double-loop interferometer with parametric flux drive and static flux breaking time-reversal symmetry. In both cases, parametric driving combined with symmetry breaking yields nonreciprocal supercurrent transport.