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We propose a novel platform for the study of quantum phase transitions in one dimension (1D QPT). The system consists of a specially designed chain of asymmetric SQUIDs; each SQUID contains several Josephson junctions with one junction shared between the nearest-neighbor SQUIDs.We develop the theoretical description of the low energy part of the spectrum. In particular, we show that the system exhibits the quantum phase transition of Ising type. In the vicinity of the transition the low energy excitations of the system can be described by Majorana fermions. This allow us to compute the matrix elements of the physical perturbations in the low energy sector. In the microwave experiments with this system, we explored the phase boundaries between the ordered and disordered phases and the critical behavior of the system's low-energy modes close to the transition. Due to the flexible chain design and control of the parameters of individual Josephson junctions, future experiments will be able to address the effects of non-integrability and disorder on the 1D QPT., Comment: 12 pages, 7 figures

We review the various theoretical arguments which strongly suggest that integer quantization of the Hall conductance holds exactly for a non-relativistic two-dimensional electron system in the presence of a static disorder and electron–electron interactions, when the chemical potential lies in a mobility gap of the system. The semi-classical picture, the Laughlin gauge-invariance argument and the connection between the Kubo Hall conductance and Chern numbers are presented, and the relevance of these idealized geometries to real systems is discussed.