The modern era of Josephson devices is strongly influenced by the combined continuous progress in material science and nanotechnologies applied to superconductivity. The capability of mixing the macroscopic phase of a superconductor and the microscopic phase of the quasi-particles through Andreev reflection keeps promoting novel phase coherent processes and functions in hybrid Josephson junctions, thus providing unique solutions to frontier problems in solid state physics and to advanced applications in quantum technologies.
We will report on a comparative study of fluctuations and electro-dynamical properties in a variety of Josephson unconventional devices. Intrinsic and poorly controlled non-equilibrium processes seem to be ubiquitous in junctions characterized by high critical current densities and invalidate the use of these junctions as quantum sensors in a variety of experiments, which intend to use the ac Josephson effect.
We define benchmarks for a classification of electro dynamical properties in presence of non-equilibrium effects based on an accurate evaluation of dissipation modes. This is of fundamental importance for the control and for the manipulation of the quantum state of a Josephson circuit, including those experiments aimed at detecting Majorana fermions and topological superconductivity through the Josephson effect. Fluctuations are thus indisputable markers of macroscopic quantum phenomena, and possibly extremely sensitive codes for novel effects.