Le sujet de thèse est une étude théorique des modes normaux d’oscillations plasma dans des chaînes de jonctions Josephson supra-conductrices. Les propriétés de ces modes normaux peuvent être contrôlés en choisissant une modulation spatiale appropriée de paramètres des jonctions le long de la chaîne et/ou un couplage approprié à l'environnement extérieur. Le travail théorique au sein du LPMMC se fait en étroite collaboration avec l'équipe expérimentale"Cohérence Quantique" à l'Institut Néel. Les problèmes spécifiques étudiés dans la thèse sont : modélisation détaillée du couplage des modes normaux à l'environnement pour leur caractérisation dans une expérience de transmission de micro-ondes, dissipation intrinsèque des oscillations du plasma à cause de quasi-particules hors équilibre, l'optimisation de la structure spatiale de la chaîne de jonctions Josephson pour son utilisation en tant qu'une super-inductance. / The subject of thesis is a theorerical study of normal modes of plasma oscillations in superconducting Josephson junction chains. The properties of these normal modes can be controlled by choosing an appropriate spatial modulation of the junction parameters along the chain and/or an appropriate coupling to the external environment. The theoretical work at LPMMC is performed in a close collaboration with the experimental Quantum Coherence group at Néel Institute. The specific problems studied in this thesis are : detailed modeling of the normal mode coupling to the environment for probing them in a microwave transmission experiment, intrinsic dissipation of plasma oscillations due to the presence of non-equilibrium quasi-particles, optimization of the spatial structure of the Josephson junction chain for its use as a super-inductance.

In this thesis, the superconductive and superresistive properties of thin percolating films of lead nanoclusters are presented. The samples were created by depositing clusters from an inert gas aggregation cluster source onto substrates held at either room temperature or 10K. Observations of the characteristic behaviours of the samples were made through R(T ) and V (I) measurements. Several interesting features were observed - smooth and discrete steps in the R(I) curves, hysteresis between increasing and decreasing bias currents, and non-zero resistances at superconducting temperatures. Explanations are proposed in terms of theoretical models of several phenomena - phase slips, phase slip centres and hotspots - which have seen little prior application to percolating systems in literature.

In this thesis, superconducting nanostructures for quantum detection of electromagnetic radiation are studied. In this regard, electrodynamics of topological excitations in 1D superconducting nanowires and 2D superconducting nanostrips is investigated. Topological excitations in superconducting nanowires and nanostrips lead to crucial deviation from the bulk properties. In 1D superconductors, topological excitations are phase slippages of the order parameter in which the magnitude of the order parameter locally drops to zero and the phase jumps by integer multiple of 2\pi. We investigate the effect of high-frequency field on 1D superconducting nanowires and derive the complex conductivity. Our study reveals that the rate of the quantum phase slips (QPSs) is exponentially enhanced under high-frequency irradiation. Based on this finding, we propose an energy-resolving terahertz radiation detector using superconducting nanowires. In superconducting nanostrips, topological fluctuations are the magnetic vortices. The motion of magnetic vortices result in dissipative processes that limit the efficiency of devices using superconducting nanostrips. It will be shown that in a multi-layer structure, the potential barrier for vortices to penetrate inside the structure is elevated. This results in significant reduction in dissipative process. In superconducting nanowire single photon detectors (SNSPDs), vortex motion results in dark counts and reduction of the critical current which results in low efficiency in these detectors. Based on this finding, we show that a multi-layer SNSPD is capable of approaching characteristics of an ideal single photon detector in terms of the dark count and quantum efficiency. It is shown that in a multi-layer SNSPD the photon coupling efficiency is dramatically enhanced due to the increase in the optical path of the incident photon.