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Searching for extremal PPT entangled states |
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| Authors: | Remigiusz Augusiak Janusz Grabowski Maciej Lewenstein |
| Affiliation: | a ICFO, Institut de Ciències Fotòniques, Parc Mediterrani de la Tecnologia, Castelldefels 08860, Spain b Faculty of Mathematics and Natural Sciences, College of Sciences, Cardinal Stefan Wyszyński University, Warszawa, Poland c Center for Theoretical Physics, Polish Academy of Sciences, Warszawa, Poland d ICREA, Institució Catalana de Recerca i Estudis Avançats, Barcelona, Spain |
| Abstract: | We study extremality in various sets of states that have positive partial transposes. One of the tools we use for this purpose is the recently formulated criterion allowing to judge if a given state is extremal in the set of PPT states. First we investigate qubit-ququart states and show that the only candidates for extremal PPT entangled states (PPTES) have ranks of the state and its partial transposition (5, 5) or (5, 6) (equivalently (6, 5)). Then, examples of extremal states of (5, 5) type and the so-called edge states of type (5, 6) are provided. We also make an attempt to explore the set of PPT states with ranks (5, 6). Finally, we discuss what are the possible configurations of ranks of density matrices and their respective partial transposition in general three-qubit and four-qubit symmetric states for which there may exist extremal entangled PPT states. For instance in the first case we show that the only possibilities are (4, 4, 4) and (4, 4, 5). |
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