The photonic cannon destroys a Borg sphere
The photonic cannon was an imaginary type of directed energy cannon, a weapon of mass destruction, created by The Doctor on board the USS Voyager, after he added daydreaming subroutines to his program. This weapon was supposedly impervious to all conventional sensors, and had enough power to destroy a Borg sphere with a single volley of two lightning-like energy beams.
The Doctor used the concept of a photonic cannon as a bluff to prevent an attack on Voyager by a Hierarchy starship, with the help of Phlox, who convinced his superior officer about the weapon's awesome power. (VOY episode: "Tinker Tenor Doctor Spy")
On November 9th in 2394, the photonic cannon was put into use for real when Starfleet completed the anti-Borg weapon for use on newer starships. (Star Trek: Intrepid)