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Updated: Jun 5, 2026

A Photonic System for Generating Unconditional Polarization-Entangled Photons Based on Multiple Quantum Interference
Published on: September 5, 2019
Experimental bound entanglement in a four-photon state
Jonathan Lavoie1, Rainer Kaltenbaek, Marco Piani
1Institute for Quantum Computing and Department of Physics and Astronomy, University of Waterloo, Waterloo, Canada.
Abstract:
Bound entanglement is central to many exciting theoretical results in quantum information processing, but has thus far not been experimentally realized. In this work, we consider a one-parameter family of four-qubit Smolin states. We experimentally produce these states in the polarization of four optical photons produced from parametric down-conversion. Within a range of the parameter, we show that our states are entangled and undistillable, and thus bound entangled. Using these bound-entangled states we demonstrate entanglement unlocking.
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