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Updated: Jan 12, 2026

Molecular Entanglement and Electrospinnability of Biopolymers
Published on: September 3, 2014
State-Entanglement-Witness Contraction
1Jagiellonian University, Universitat Autònoma de Barcelona, Physics Department, ES-08193 Bellaterra (Barcelona), Spain and Faculty of Physics, Astronomy and Applied Computer Science, Institute of Theoretical Physics, 30-348 Kraków, Poland.
Abstract:
We construct linear and nonlinear entanglement witnesses, by tensoring and partial tracing existing states and witnesses. We show that little shared quantum resources allow one to employ decomposable witnesses to obtain larger ones detecting locally undistillable states and find analytic witnesses for multipartite entangled states that are undistillable across all bipartitions. Crucially, we show how to efficiently optimize multicopy witnesses to desired states, which is a current challenge. As an example of both theoretical and experimental interest, existing trace polynomial witnesses are significantly improved while preserving their symmetries and implementability with randomized measurements. In addition to detecting entanglement, we also find new witnesses detecting k-copy distillability. A recipe for the single-copy case is shown to be effective for generic and Werner states.
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