Correction to: Nature Physics https://doi.org/10.1038/s41567-018-0141-9, published online 21 May 2018.

In the version of this Article originally published, A. Mollén’s affiliation was incorrectly denoted as number 10; it should have been 1. Throughout the Article, the tilde symbol above b was too high to be visible. In the second column of page five, the superscript 2 in \(\kappa \equiv ((\epsilon _t/\tilde b_{10})^2)\) was also too high to be visible. Finally, the citation to ref. 35 on page one of the Supplementary Information was incorrect; it should have been to ref. 36. These issues have now been corrected.