Dynamic properties of high-Tc superconducting nano-junctions made with a focused helium ion beam

TL;DR

This paper investigates the dynamic and noise properties of high-temperature superconducting nano-junctions fabricated with a helium ion beam, demonstrating their potential for low-noise microwave and terahertz applications.

Contribution

It introduces a fabrication method for high-$T_{c}$ Josephson nano-junctions and characterizes their noise and frequency properties, showing their suitability for high-frequency quantum devices.

Findings

Current-voltage follows RSJ model

Characteristic frequency reaches ~300 GHz

Josephson oscillation linewidth limited by thermal noise

Abstract

The Josephson junction (JJ) is the corner stone of superconducting electronics and quantum information processing. While the technology for fabricating low $T_{c}$ JJ is mature and delivers quantum circuits able to reach the "quantum supremacy", the fabrication of reproducible and low-noise high-$T_{c}$ JJ is still a challenge to be taken up. Here we report on noise properties at RF frequencies of recently introduced high-$T_{c}$ Josephson nano-junctions fabricated by mean of a Helium ion beam focused at sub-nanometer scale on a $\mathrm{YBa}_2\mathrm{Cu}_3\mathrm{O}_7$ thin film. We show that their current-voltage characteristics follow the standard Resistively-Shunted-Junction (RSJ) circuit model, and that their characteristic frequency $f_{c}=(2e/h)I_{c}R_{n}$ reaches $\sim 300$ GHz at low temperature. Using the "detector response" method, we evidence that the Josephson oscillation linewidth is only limited by the thermal noise in the RSJ model for temperature ranging from $T\sim 20$ K to $75$ K. At lower temperature and for the highest He irradiation dose, the shot noise contribution must also be taken into account when approaching the tunneling regime. We conclude that these Josephson nano-junctions present the lowest noise level possible, which makes them very promising for future applications in the microwave and terahertz regimes.