well, a Standard Photon is 64 megatons and a Quantum is 3x that power, making it 192 megatons. A Sovereign has a Rapid Launcher which fires four torpedoes per-shot, so in one attack the Sovereign would unleash 768 megatons of power. And since the Quantums have Zero-Point Technology, 100% of the blast would impact into the ship and shields. They could also fire from long range and out maneuver that ship.