Dependence of the Macroscopic Quantum Tunneling Rate on Josephson Junction Area

TL;DR

This study systematically investigates how the size of Nb/Al-AlO_x/Nb Josephson junctions affects the macroscopic quantum tunneling rate, revealing a size-dependent crossover temperature consistent with theoretical predictions.

Contribution

It provides the first detailed experimental analysis of the dependence of MQT rates on junction area in Nb-based Josephson junctions, with environmental decoupling techniques.

Findings

Crossover temperature decreases with increasing junction area.

Experimental results agree with theoretical models.

Environmental decoupling enables precise MQT measurements.

Abstract

We have carried out systematic Macroscopic Quantum Tunneling (MQT) experiments on Nb/Al-AlO_x/Nb Josephson junctions (JJs) of different areas. Employing on-chip lumped element inductors, we have decoupled the JJs from their environmental line impedances at the frequencies relevant for MQT. This allowed us to study the crossover from the thermal to the quantum regime in the low damping limit. A clear reduction of the crossover temperature with increasing JJ size is observed and found to be in excellent agreement with theory. All junctions were realized on the same chip and were thoroughly characterized before the quantum measurements.