A key resource in future quantum communication networks is entanglement: a quantum correlation that can be developed between, for example, distant nodes of the network. Special methods of measuring the nodes’ state can create the entanglement or protect an already existing entanglement against destructive environmental effects. Scientists led by Gerhard Rempe at the Max Planck Institute for Quantum Optics (MPQ) in Germany have implemented such a measurement on two distant atomic qubits. The final state of the qubits has 67 percent “fidelity” to an ideally entangled state.
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