Enhancement of Josephson phase diffusion by microwaves

TL;DR

This paper investigates how microwave radiation enhances phase diffusion in small Josephson junctions, revealing a peak in current-voltage characteristics that evolves into Shapiro steps, supported by experimental and theoretical analysis.

Contribution

It provides the first detailed experimental and theoretical analysis of microwave-induced enhancement of phase diffusion in Josephson junctions.

Findings

Microwave radiation causes a pronounced current peak in I-V characteristics.

The peak voltage scales as the square root of microwave power.

The peak evolves into Shapiro steps with increasing frequency.

Abstract

We report an experimental and theoretical study of the phase diffusion in small Josephson junctions under microwave irradiation. A peculiar enhancement of the phase diffusion by microwaves is observed. The enhancement manifests itself by a pronounced current peak in the current-voltage characteristics. The voltage position $V_{\rm top}$ of the peak increases with the power $P$ of microwave radiation as $V_{\rm top}\propto\sqrt P$, while its current amplitude weakly decreases with $P$. As the microwave frequency increases, the peak feature evolves into Shapiro steps with finite slope. Our theoretical analysis taking into account the enhancement of incoherent superconducting current by multi-photon absorption is in good agreement with experimental data.