We present an experimental realization of the Smolin state using hyperentangled photon pairs from spontaneous parametric downconversion, to our knowledge the first optical demonstration of bound entanglement that does not simulate mixture using random unitaries.
Quantum entanglement exhibits various interesting features that emerge only in high-dimensional systems. One of the most fascinating is bound entanglement, entanglement that cannot be extracted using local operations and classical communication. This thesis describes our work towards an experimental realization of the four-qubit bound-entangled Smolin state, using the polarization and spatial mode of photon pairs. We describe a number of interesting experimental challenges that this work faced. We present our results on entangled two-qubit spatial mode states and hyperentangled four-qubit polarization-spatial-mode states generated by spontaneous parametric down-conversion from a second-order TEM mode pump. Some of the subtleties involved in preparing genuine mixed states in the lab are discussed.
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.