NLO in the large charge sector of the critical $O(N)$ model at large $N$

We compute the next-to-leading correction to the scaling dimension of large-charge operators in the $3d$ critical $O(N)$ model in a double scaling limit in which both $N$ and the operator charge $Q$ are taken to be large. When $Q\gg N$ our result matches predictions from the conformal superfluid EFT and allows to extract next-to-leading order corrections to the EFT Wilsonian coefficients. At present, our result represents the most precise determination of large-charge operator scaling dimension in weakly-coupled CFTs.