Integrable systems and AdS/CFT duality

This PhD thesis explores the similarities between integrable spin chains and quantum field theories, such as Super Yang Mills. We first study integrable spin chains and build explicitly a polynomial "Backlund flow" and polynomial "Q-operators", which allow to diagonalize the Hamiltonian. We then study integrable field theories et show how to obtain "Q-functions", analogous to the Q-operators built for spin chains. It turns out that several important informations are contained in the analytic properties of these Q -functions. That allows to obtain, in the framework of the thermodynamic Bethe ansatz, a finite number of non-linear integral equations encoding the finite-size spectrum of the theory which we study. This system of equations is equivalent to an infinite system of equations, known as "Y-system", which had been quite recently conjectured in the case of the AdS/CFT duality.