Circles and arcs use polylines to represent them. To smooth them out increase the resolution. To set the global resolution for your 2D geometry, go to Preferences -> Display and set curves to a higher resolution. To set one or more curves to a non-default resolution, hold the Shift key and select all the curves to be changed then right-click on one of the curves and in the popup menu set the desired resolution. To change one curve just right-click on it.