Correction to: Nature Physics https://doi.org/10.1038/s41567-019-0704-4, published online 11 November 2019; corrected online 21 November 2019.

In the version of this Article originally published online, and in the later correction, the first equation in the sentence beginning “One popular approach is” was incorrect; the correct equation is ‘\(- \partial _\beta \left| {{{\varPhi }}\left( \beta \right)} \right\rangle = \hat H\left| {{{\varPhi }}\left( \beta \right)} \right\rangle\)’. This has now been amended in all versions of the Article.