Interplay of bound states in the continuum and Fano-Andreev interference in a hybrid triple quantum dot.

We investigate bound states in the continuum (BICs) in a hybrid normal-superconducting triple quantum dot system, where the central dot is coupled to two normal leads and the lateral dots are proximity-coupled to superconducting electrodes. Local electron-electron interactions are treated within the Hubbard-I approximation. Finite bias probes Fano-Andreev interference between the direct elastic tunneling path through the central dot and indirect proximity-induced paths involving the lateral dots, revealing an Andreev-type BIC in the symmetric limit and its crossover into a quasi-BIC when lateral-dot detuning mixes the dark and bright sectors. As the bias is swept through the subgap resonances, electron transmission (ET) exhibits sharp antiresonances that evolve into near-zero transmission minima, signaling the transport fingerprints of (quasi-)BICs. We further find a continuous crossover from a Fano-Andreev BIC-supported regime to a Fano-Andreev quasi-BIC regime as the lateral-dot detuning increases. The formation of BICs and quasi-BICs is accompanied by a bias-dependent redistribution of the occupations of the side quantum dots, providing an internal diagnostic directly correlated with the transport signatures of the bound states.