Heteroatomic Andreev Molecule in a Superconducting Island-Double Quantum Dot Hybrid.

Topological superconductors (SCs) hold great promise for fault-tolerant quantum hardware; however, their experimental realization is very challenging. Recently, superconducting artificial molecules (Andreev molecules) have opened new avenues to engineer topological superconducting materials. In this work, we demonstrate a heteroatomic Andreev molecule, where two normal artificial atoms realized by quantum dots (QDs) are coupled by a superconducting island (SCI). We show that the two normal atoms hybridize and form a three-electron-based molecular state. Our density matrix renormalization group (DMRG) calculations explain quantitatively the robust binding of electrons. The tunability of the structure allows us to drive a quantum phase transition from an antiferromagnetic Andreev molecular state to a heteroatomic Andreev molecule with ferromagnetically coupled QDs using simple electrical gating.