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Updated: May 16, 2026

A Photonic System for Generating Unconditional Polarization-Entangled Photons Based on Multiple Quantum Interference
Published on: September 5, 2019
Detection of multiparticle entanglement: quantifying the search for symmetric extensions
Fernando G S L Brandão1, Matthias Christandl
1Institute for Theoretical Physics, ETH Zurich, Wolfgang-Pauli-Strasse 27, 8097 Zurich, Switzerland.
Abstract:
We provide quantitative bounds on the characterization of multiparticle separable states by states that have locally symmetric extensions. The bounds are derived from two-particle bounds and relate to recent studies on quantum versions of de Finetti's theorem. We discuss algorithmic applications of our results, in particular a quasipolynomial-time algorithm to decide whether a multiparticle quantum state is separable or entangled (for constant number of particles and constant error in the norm induced by one-way local operations and classical communication, or in the Frobenius norm). Our results provide a theoretical justification for the use of the search for symmetric extensions as a test for multiparticle entanglement.
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