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Efficient Cooper pair splitting without interactions
For the three-terminal NSN device with single-mode normal terminals and without Coulomb blockade, we propose the interpretation of charge transfer process, which allows us to consistently characterize the device operation as that of a Cooper pair splitter in terms of scattering matrix elements as well as in terms of measurable quantities. The obtained explicit expression for the splitting probability notably contains the two-particle interference term not available from conductance measurements. We show that splitting does not necessarily rely on single-particle crossed Andreev reflection amplitude thus allowing for the unit efficiency at zero energy. Our results imply that the current cross correlator generally does not provide definite measure of splitting.