Schematic representation of one iteration step of the entanglement purification process. The diamond shaped elements denote acceptance of the pair of qubits only when both measurements yield 0. The depicted procedure is used to prepare from an ensemble E′ made up of pairs of qubits all in a state |ψ〉, an ensemble E made made up of pairs of qubits in the state |ψ′〉. During the procedure, half of the pairs in E are completely used up, while a portion of the other half is retained depending on the measurement outcome. H is the Hadamard gate.
Convergence of given initial states to the two limiting cycles as a function of the complex parameter ζ. The blue color denotes convergence to a maximally entangled state, and the green color the convergence to the cycle of the two separable states.