Correction to: Nature Physics, published online 11 November 2019.

In the version of this Article originally published online, in the first equation in the sentence beginning “One popular approach is”, the term ‘\(- \partial _\beta \left| {\it{\varPhi} \left( \beta \right)} \right\rangle =\)’ was repeated; the equation should have read “\(- \partial _\beta \left| {\it{\varPhi} \left( \beta \right)} \right\rangle = \left\{ {\left| \it{\varPhi} \right\rangle ,\;\hat H\left| \it{\varPhi} \right\rangle ,\hat H^2\left| \it{\varPhi} \right\rangle \ldots } \right\}\left| {\it{\varPhi} \left( \beta \right)} \right\rangle\)”. In the same sentence, in the expression “〈Φ(0)|Ψ ≠ 0”, the right ket bracket was missing and should have read ‘〈Φ(0)|Ψ〉≠ 0’’. All versions of this Article have been amended.