The quantum torpedo is a high-yield Starfleet projectile introduced in the 2370s, carried by front-line ships such as the Defiant and the Enterprise-E alongside photon torpedoes.
Quantum torpedoes were developed as a more powerful successor to the photon torpedo and became part of the arsenal of new warships in the 2370s. They deliver a considerably higher yield than photon torpedoes and were fitted to ships designed with combat against the Borg and the Dominion in mind.
The USS Defiant carried them in its battles against the Dominion, and the Sovereign-class Enterprise-E fired them during the Borg attack on Earth in 2373. Photon torpedoes remained in widespread use, and many ships carried both.