Universal spectral features of ultrastrongly coupled systems

We identify universal properties of the low-energy subspace of a wide class of quantum optical models in the ultrastrong coupling limit, where the coupling strength dominates over all other energy scales in the system. We show that the symmetry of the light-matter interaction is at the origin of a twofold degeneracy in the spectrum. We prove analytically this result for bounded Hamiltonians and extend it to a class of models with unbounded operators. As a consequence, we show that the emergence of superradiant phases previously investigated in the context of critical phenomena, is a general property of the ultrastrong coupling limit. The set of models we consider encompasses different scenarios of possible interplay between critical behavior and superradianceS. F. acknowledges support from the European Research Council (ERC-2016-STG-714870

Contacting diffusion with FIB for backside circuit edit procedures and material analysis

Contacting Diffusion with FIB for Backside Circuit Edit Procedures and Material Analysi