Tuning the inductance of Josephson junction arrays without SQUIDs

TL;DR

This paper presents a method to tune the inductance of Josephson junction arrays without using SQUIDs by exploiting magnetic field focusing effects, simplifying device design and enabling higher inductance densities.

Contribution

The authors demonstrate a SQUID-free Josephson junction array with tunable inductance via magnetic field focusing, offering a simpler and denser alternative to traditional SQUID-based devices.

Findings

Achieved magnetic field-tunable inductance in SQUID-free arrays.

Demonstrated a transmission line with impedance tunable between 4-8 kΩ.

Enabled higher inductance per unit length compared to SQUID-based designs.

Abstract

It is customary to use arrays of superconducting quantum interference devices (SQUIDs) for implementing magnetic field-tunable inductors. Here, we demonstrate an equivalent tunability in a (SQUID-free) array of single Al/AlOx/Al Josephson tunnel junctions. With the proper choice of junction geometry, a perpendicularly applied magnetic field bends along the plane of the superconductor and focuses into the tunnel barrier region due to a demagnetization effect. Consequently, the Josephson inductance can be efficiently modulated by the Fraunhoffer-type supercurrent interference. The elimination of SQUIDs not only simplifies the device design and fabrication, but also facilitates a denser packing of junctions and, hence, a higher inductance per unit length. As an example, we demonstrate a transmission line, the wave impedance of which is field-tuned in the range of $4-8~\textrm{k}\Omega$, centered around the important value of the resistance quantum $h/(2e)^2 \approx 6.5~\textrm{k}\Omega$.