We report the creation of Greenberger-Horne-Zeilinger states with up to 14 qubits. By investigating the coherence of up to 8 ions over time, we observe a decay proportional to the square of the number of qubits. The observed decay agrees with a theoretical model which assumes a system affected by correlated, Gaussian phase noise. This model holds for the majority of current experimental systems developed towards quantum computation and quantum metrology.
@article{arxiv.1009.6126,
title = {14-qubit entanglement: creation and coherence},
author = {Thomas Monz and Philipp Schindler and Julio T. Barreiro and Michael Chwalla and Daniel Nigg and William A. Coish and Maximilian Harlander and Wolfgang Haensel and Markus Hennrich and Rainer Blatt},
journal= {arXiv preprint arXiv:1009.6126},
year = {2011}
}