Learning Linear-Quadratic Regulators Efficiently with only $\sqrt{T}$ Regret

We present the first computationally-efficient algorithm with $\widetilde O(\sqrt{T})$ regret for learning in Linear Quadratic Control systems with unknown dynamics. By that, we resolve an open question of Abbasi-Yadkori and Szepesv\ári (2011) and Dean, Mania, Matni, Recht, and Tu (2018).