A recent study has challenged the ability of conductance measurements to differentiate between crossed Andreev reflection (CAR) and elastic co-tunneling (EC) in normal-superconductor-normal (NSN) junctions. Both processes involve charge transport across the interface between a normal metal and a superconductor, but their underlying physical mechanisms are distinct, and their correct identification is crucial for the development of quantum devices.

Crossed Andreev reflection occurs when an electron from one normal contact impinges on a superconductor, and instead of reflecting as a hole in the same contact, it pairs with another electron to form a Cooper pair, and the resulting hole emerges in a different normal contact. This process is fundamental for the creation of spin-entangled states and has direct implications for quantum computing. On the other hand, elastic co-tunneling is a charge transport process in which an electron tunnels from one normal contact to another through the superconductor, without forming a Cooper pair, maintaining its energy and spin. The difficulty lies in the fact that both mechanisms can produce very similar conductance signatures, complicating their experimental discrimination.