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

Authors: 
Hendrik Meier, R. T. Brierley, Angela Kou, S. M. Girvin, and Leonid I. Glazman
Name of the Journal: 
Phys. Rev. B
Date of Pub: 
August 24, 2015
Year of Publication: 
2015
Volume: 
92
Issue: 
6
Pages: 
064516
Publisher Name, Address and Year: 
American Physical Society
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.