Nonequivalence between absolute separability and positive partial transposition in the symmetric subspace

Abstract

The equivalence between absolutely separable states and absolutely positive partial transposed (PPT) states in general remains an open problem in quantum entanglement theory. In this work, we study an analogous question for symmetric multiqubit states. We show that symmetric absolutely PPT (SAPPT) states (symmetric states that remain PPT after any symmetry-preserving unitary evolution) are not always symmetric absolutely separable by providing explicit counterexamples. More precisely, we construct a family of entangled five-qubit SAPPT states. Similar counterexamples for larger odd numbers of qubits are identified.

9 pages, 2 figure

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• On the extreme points of sets of absolulely separable and PPT states
• Bound entanglement in symmetric random induced states
• Detection of nonabsolute separability in quantum states and channels through moments