Experimental four-qubit bound entanglement

최정운

Jonathan Lavoie, Rainer Kaltenbaek, Marco Piani +1 more

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.

Ryszard Horodecki

leven years later, on 23 rd August 2009, Nature Physics [1] reported that the researchers of a laboratory in Stockholm had created a four-qubit bound entangled state.Another eight months later, on 30 th April, another team from the laboratory in Dortmund reported the creation of pseudo-bound entanglement [2].When that paper was in preparation, a team of researchers from Waterloo (see Fig. 1) announced [3] that they had managed to experimentally create a genuine bound entangled state.At the same time the Innsbruck group presented an experiment implementing bound entanglement with ions [4].e exciting course of these events already shows that experimental, unrecoverable imprisoning of quantum correlations,even in the simplest (four-qubit) arrangement, is no small challenge.At the current stage, full understanding of bound entanglement -"a mysterious invention of nature"[5] -may be no more than an illusion.Nevertheless, it is interesting to follow the paths that led to that invention in a foggy bush of quantum formalism,in order properly to appreciate the efforts and inventiveness of experimentalists.

F.J. Duarte

Aditya N. Sharma

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.

Michael Shulman