Pulsars are highly magnetized and rapidly rotating neutron stars. The magnetic field can reach the critical magnetic field from which quantum effects of the vacuum becomes relevant, giving rise to magnetooptic properties of vacuum characterized as an
effective non linear medium. One spectacular consequence of this prediction is a macroscopic friction that leads to an additional contribution in the spindown of pulsars. In this paper, we highlight some observational consequences and in particular derive new constraints on the parameters of the Crab pulsar and J0540-6919.
