At it's core what they are doing is really simple. If you have ever played with magnets, you know that when you have two like poles they repel each other. If you put electricity through a wire you can create a magnetic field. What they did was turn the coil that surround the quarter, and the quarter itself into really strong magnets. Since the magnetic fields were repelling each other push on the quarter in all directions, shrinking it.
This is cool science in action!