I want to represent parallel transport as in the following figure, but next to this figure I would like to place a diagram with the two arrows (of the initial state and of the final state that are present at the top of the spherical surface) and the angle between them, to see better and put more emphasis on the analogy with the Berry phase.
How can I draw the two arrows and the angle? Is there a program that allows me to do this and is free? What programs do you use to draw images from scratch and are free (and provide good images for example, to put in articles)?
The image was taken from this thesis.