# Insulating Josephson-junction chains as pinned Luttinger liquids

## TL;DR

This paper experimentally demonstrates that disordered Josephson-junction chains behave as pinned Luttinger liquids, confirming theoretical predictions and revealing their potential as a one-dimensional Bose glass with implications for quantum standards.

## Contribution

It provides the first experimental evidence that disordered Josephson-junction chains act as pinned Luttinger liquids, validating key quantum many-body theories.

## Key findings

- Insulating Josephson-junction chains are pinned Luttinger liquids.
- Chains exhibit behavior consistent with a Bose glass phase.
- Results impact the development of quantum current standards.

## Abstract

Quantum physics in one spatial dimension is remarkably rich, yet even with strong interactions and disorder, surprisingly tractable. This is due to the fact that the low-energy physics of nearly all one-dimensional systems can be cast in terms of the Luttinger liquid, a key concept that parallels that of the Fermi liquid in higher dimensions. Although there have been many theoretical proposals to use linear chains and ladders of Josephson junctions to create novel quantum phases and devices, only modest progress has been made experimentally. One major roadblock has been understanding the role of disorder in such systems. We present experimental results that establish the insulating state of linear chains of sub-micron Josephson junctions as Luttinger liquids pinned by random offset charges, providing a one-dimensional implementation of the Bose glass, strongly validating the quantum many-body theory of one-dimensional disordered systems. The ubiquity of such an electronic glass in Josephson-junction chains has important implications for their proposed use as a fundamental current standard, which is based on synchronisation of coherent tunnelling of flux quanta (quantum phase slips).