Positive noise cross-correlation in hybrid superconducting and normal-metal three-terminal devices

Non-local entanglement is a key ingredient to quantum information processing. For photons, entanglement has been demonstrated(1), but it is more difficult to observe for electrons. One approach is to use a superconductor, where electrons form spin-entangled Cooper pairs, which is a natural source for entangled electrons. For a three-terminal device consisting of a superconductor sandwiched between two normal metals, it has been predicted that Cooper pairs can split into spin-entangled electrons flowing in the two spatially separated normal metals(2-5), resulting in a negative non-local resistance and a positive current-current correlation(6,7). The former prosperity has been observed(8,9), but not the latter. Here we show that both characteristics can be observed, consistent with Cooper-pair splitting. Moreover, the splitting efficiency can be tuned by independently controlling the energy of the electrons passing the two superconductor/normal-metal interfaces, which may lead to better understanding and control of non-local entanglement.