Signatures of quantum phase transitions in the dynamic response of fluxonium qubit chains

TL;DR

This paper investigates how the dynamic microwave response of fluxonium qubit chains reveals quantum phase transitions, highlighting the signatures of soft modes and the influence of quantum fluctuations on the phase diagram.

Contribution

It provides a detailed analysis of the phase diagram of fluxonium chains and identifies observable signatures of phase transitions in their admittance spectra.

Findings

Identification of phase transition signatures in admittance spectra

Observation of inhomogeneous persistent currents in certain phases

Quantum fluctuations lead to gapless floating phases

Abstract

We evaluate the microwave admittance of a one-dimensional chain of fluxonium qubits coupled by shared inductors. Despite its simplicity, this system exhibits a rich phase diagram. A critical applied magnetic flux separates a homogeneous ground state from a phase with a ground state exhibiting inhomogeneous persistent currents. Depending on the parameters of the array, the phase transition may be a conventional continuous one, or of a commensurate-incommensurate nature. Furthermore, quantum fluctuations affect the transition and possibly lead to the presence of gapless "floating phases". The signatures of the soft modes accompanying the transitions appear as a characteristic frequency dependence of the dissipative part of admittance.