The ATLAS experiment at the Large Hadron Collider has performed precise measurements of mixing and CP violation in neutral B mesons. The Standard Model predicts the CP-violating mixing phase $\phi_s$, to be very small and its SM value is very well constrained, while any measured deviations from SM value can indicate New Physics not described by the SM.
The future analyses will profit considerably from the increased statistics expected from the $3 000 ~\mathrm{fb^{-1}}$ of HL-LHC data as well as detector improvements providing better mass and proper decay time resolutions.
This contribution focuses on the latest results from ATLAS, including measurements of CP violation in the $B_s^0 \to J/\psi \phi$ channel, and the prospects of future analyses of the same channel.