Correction to: Nature Physics https://doi.org/10.1038/s41567-018-0275-9, published online 10 September 2018.

In the version of this Letter originally published, the Supplementary Videos were incorrectly labelled; the descriptions of 1–4 should have gone with the videos of 6–9, and the descriptions of 5–9 should have gone with the videos of 1–5. This has now been corrected.