Speaker
Description
Stability–efficiency trade-offs in nonequilibrium transport are constrained by thermodynamic uncertainty relations (TURs), which bound current fluctuations in terms of entropy production. In hybrid normal–superconducting (N–S) devices, however, the status of quantum TURs has remained unclear. Here we investigate Andreev-mediated transport and fluctuations in N–S junctions and quantum-dot systems, including the effects of superconducting coherence and Coulomb interactions. In the subgap (Andreev) regime, we show that deviations from the normal quantum TUR are governed by macroscopic superconducting coherence quantified by the pair amplitude, while dephasing or interactions suppress this coherence and restore conventional bounds. We derive a hybrid quantum TUR valid for all two-terminal N–S junctions in the Andreev regime, which is never violated, is saturated only at vanishing current, and connects to the normal quantum bound via the substitution e —> 2e. Using real-time diagrammatics and full counting statistics, we compute current, noise, and entropy production for interacting N–S quantum dots in the large-gap limit. Coulomb interactions renormalize resonant transport and strongly reduce current precision, especially at high temperatures where average currents are weakly affected. Our results establish a direct link between superconducting coherence, interactions, and nonequilibrium fluctuations, and identify current precision as a robust probe of interacting Andreev transport.