Coherence of large-scale entanglement

We report the creation of large Schroedinger-Cat states with up to 14 qubits. By investigating their coherence over time, we observe a decay proportional to the square of the number of qubits. The observed decay agrees with our theoretical model which assumes a system affected only by correlated, Gaussian phase noise. Our model holds for the majority of current experimental systems developed towards quantum computation and quantum metrology.