Hyperinductance based on stacked Josephson junctions

TL;DR

This paper introduces two scalable fabrication methods for superinductances based on stacked Josephson junctions, achieving high impedance and inductance suitable for advanced quantum circuits.

Contribution

It presents novel fabrication techniques for superinductances using stacked Josephson junctions, demonstrating high impedance and scalability for quantum applications.

Findings

Achieved a characteristic impedance of ~16 kΩ with nine junctions per stack.

Demonstrated √n impedance scaling with the number of junctions.

Fabricated high-impedance chains with inductance of 5.9 μH at microwave frequencies.

Abstract

Superinductances are superconducting circuit elements that combine a large inductance with a low parasitic capacitance to ground, resulting in a characteristic impedance exceeding the resistance quantum $R_Q = h/(2e)^2 \simeq 6.45 \mathrm{k}\Omega$. In recent years, these components have become key enablers for emerging quantum circuit architectures. However, achieving high characteristic impedance while maintaining scalability and fabrication robustness remains a major challenge. In this work, we present two fabrication techniques for realizing superinductances based on vertically stacked Josephson junctions. Using a multi-angle Manhattan (MAM) process and a zero-angle (ZA) evaporation technique -- in which junction stacks are connected pairwise using airbridges -- we fabricate one-dimensional chains of stacks that act as high-impedance superconducting transmission lines. Two-tone microwave spectroscopy reveals the expected $\sqrt{n}$ scaling of the impedance with the number of junctions per stack. The chain fabricated using the ZA process, with nine junctions per stack, achieves a characteristic impedance of $\sim 16 \mathrm{k}\Omega$, a total inductance of $5.9 \mathrm{\mu H}$, and a maximum frequency-dependent impedance of $50 \mathrm{k}\Omega$ at 1.4 GHz. Our results establish junction stacking as a scalable, robust, and flexible platform for next-generation quantum circuits requiring ultra-high impedance environments.