Bloch Sphere Animations
Basic Hahn Echo (big spread in frequencies)
90x - Delay - 180y - Echo
Because of a spread in the spin precession frequencies, we see different precession rates in any given rotating frame. In this frame, red spins always go counterclockwise while blue spins always go clockwise. The bright purple arrow is the vector sum. Watch as it shrinks along the y-axis and then grows again forming the echo.