Nature Communications 5: Article Number: 5163 10.1038/ncomms6163 (2014); Published: 16 October 2014; Updated: 19 November 2014.

This Article contains an error in Fig. 1 that was introduced during the production process. The pulse waveforms were displayed in white colour, making some of them invisible against the background. The correct version of Fig. 1 appears below.

figure 1