Gate-controlled Elastic Co-Tunneling and Crossed Andreev Reflection mediated by Andreev Bound States

Elastic co-tunneling (ECT) and crossed Andreev reflection (CAR) are complementary processes that take place when two normal leads are separated by a thin superconductor. In the former, an electron hops from one lead to another, and in the latter, two correlated electrons from both sides enter or leave the superconducting segment. Controlling the ECT and CAR amplitudes and extending the range over which they can occur is desirable to couple spin qubits and form artificial topological structures such as the Kitaev chain. We fabricate and measure CAR and ECT in an InSb nanowire device, where two quantum dots are separated by a superconducting segment. We show by comparison to a theoretical model that both ECT and CAR are mediated by an Andreev bound state (ABS) residing under the superconducting segment. Since ECT and CAR are mediated by the ABS, we show that they extend beyond the superconducting coherence length, and their amplitudes are tuned by external plunger gate and magnetic field. This tunability is an essential tool for the future engineering of topological superconductivity in meta-materials.