Mixed-State Entanglement and Distillation: Is there a “Bound” Entanglement in Nature?

TLDR

The paper discusses the possible physical implications of the result. The study shows that a mixed state can be distilled to a singlet only if it violates the partial transposition criterion, revealing two distinct entanglement types: free (distillable) and bound (non‑distillable). The result is based on Peres, Phys.

Abstract

It is shown that if a mixed state can be distilled to the singlet form, it must violate partial transposition criterion [A. Peres, Phys. Rev. Lett. 76, 1413 (1996)]. It implies that there are two qualitatively different types of entanglement: ``free'' entanglement which is distillable, and ``bound'' entanglement which cannot be brought to the singlet form useful for quantum communication purposes. Possible physical meaning of the result is discussed.