Remarks on 2–q-bit states
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- Englert, BG. & Metwally, N. Appl Phys B (2001) 72: 35. doi:10.1007/s003400000502
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We distinguish six classes of families of locally equivalent states in a straightforward scheme for classifying all 2–q-bit states; four of the classes consist of two subclasses each. The simple criteria that we stated recently for checking a given state’s positivity and separability are justified, and we discuss some important properties of Lewenstein–Sanpera decompositions. An upper bound is conjectured for the sum of the degree of separability of a 2–q-bit state and its concurrence.