# Microwave spectroscopy of a weakly-pinned charge density wave in a superinductor

## TL;DR

This study investigates the microwave response of a superinductor, revealing its behavior as a weakly-pinned charge density wave within the Bose glass universality class, bridging high- and low-frequency excitations.

## Contribution

It demonstrates that superinductors exhibit Bose glass characteristics, linking microwave scattering data to charge density wave dynamics in superconducting devices.

## Key findings

- Microwave reflection amplitude relates to Bose glass dynamics.
- Transition from plasmon modes to pinned charge density wave spectrum.
- Identification of Larkin pinning length effects on microwave response.

## Abstract

A chain of small Josephson junctions (aka superinductor) emerged recently as a high-inductance, low-loss element of superconducting quantum devices. We notice that the intrinsic parameters of a typical superinductor in fact place it into the Bose glass universality class for which the propagation of waves in a sufficiently long chain is hindered by pinning. Its weakness provides for a broad crossover from the spectrum of well-resolved plasmon standing waves at high frequencies to the low-frequency excitation spectrum of a pinned charge density wave. We relate the scattering amplitude of microwave photons reflected off a superinductor to the dynamics of a Bose glass. The dynamics at long and short scales compared to the Larkin pinning length determines the low- and high-frequency asymptotes of the reflection amplitude.