It clones antimatter, applies high pressure, and then speeds it down the "barrel." But it hardly produces any pressure. Why? When antimatter vaporizes a particle, it emits a very small area of extremely low pressure. Since the size of the pressure generator is almost the same size as all the particles being cut all together, they cancel each other out perfectly.
The best part, however, is the fact that it produces no change it temperature. So now you can have clean lines down any destructible material, with no heat, no fire, and no issues.