Figure 1: (a) Andreev reflection, where an electron in a normal metal is reflected as a hole, and a pair is transmitted to a superconductor. (b)–(d) Tunneling processes between a superconductor and two normal metal arms that are separated by less than the superconducting coherence length: (b) Electrons from a superconducting pair tunnel into different arms (equivalent to crossed Andreev reflection), demonstrating nonlocal entanglement; (c) pair transport into a single arm; (d) elastic co-tunneling. Tunneling into quantum dots can suppress processes (c) and (d).