Experimental demonstration of entanglement robustness in four-qubits entangled system
Mohamed Bourennane, Manfred Eibl, Sascha Gaertner, Christian Kurtsiefer, Harald Weinfurter · 2004
The paper concentrates on a particular four-qubit entangled state which can be directly prepared experimentally by spontaneous parametric down-conversion. Peres-Horodecki criterion is applied, which states that for separable states p, the partial transpose of the density matrix /spl rho/ must have nonnegative eigenvalues.