Dr. Luka Pavešič (IJS, FMF): Tiny superconductors and quantum dots: interplay of superconductivity and magnetism in quantum devices

Quantum devices where a superconductor is coupled to a semiconducting quantum dot are a tunable playground for probing the competition between two fundamental types of quantum order: superconductivity and magnetism. Their interplay is reflected in the presence of discrete and long-lived states inside the superconducting gap. These can in turn be used for applications in quantum technologies, most notably as enhanced superconducting qubits. In modern realisations, the constituent parts of such devices are small enough that a third effect comes into play --- the Coulomb repulsion between tightly confined electrons leads to capacitive effects. These qualitatively change the physics in a way that is largely incompatible with the standard mean-field BCS model of superconductivity. After introducing the basics I will present a particle-number conserving theory of superconductivity in this context, and show how we use it to model tiny quantum devices.
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