Quantum Singularity
A Quantum Singularity is a term commonly used by 24th century Federation starship personnel to refer to a point or region in the space-time continuum where normal physical models do not apply and extraordinary amounts of gravitational forces are typically present. Singularities can be both natural and artificial: wormholes, quantum matrices of planets, and black holes all can contain singularities, as do certain reactors (for example, those found in Romulan starships).
Singularities can be detected by the effect they have on local gravimetric field signatures nearby (although they can be buried so far down in subspace layers that they cannot be detected in that way), and/or by using tetryon emissions as a guide. Singularities in general, and quantum singularities in particular, are known by 24th century science even when stable to send out waves of temporal displacement that affects, among other things, delta-series radioisotopes. Also, energy emitted by an exploding microscopic singularity can shift chroniton particles into a high state of temporal polarization and create subspace bubbles around nearby starships. This latter result can cause temporal anomalies and was directly observed by the USS Defiant in 2371. (DS9: "Visionary", "Past Tense, Part I")
One example of the use of a singularity was demonstrated in 2373. The Borg, Species 8472, and the USS Voyager were all able to travel between the fluidic space dimension and our dimension via artificially created quantum singularities. (VOY: "Scorpion", "Scorpion, Part II")
Another, very unusual, use of a singularity was in 2377 when Voyager bounced a tachyon beam off a singularity to permit real-time communication between the Alpha Quadrant and the Delta Quadrant. (VOY: "Author, Author")
The artificial quantum singularity (also referred to as a confined or forced quantum singularity) was a method of generating energy.
In the 24th century, artificial quantum singularities served as the primary power source for large Romulan spacecraft, such as the D'deridex Class warbird. Once activated, the singularity core cannot be shut down. (TNG: "Face of the Enemy", "Timescape"; DS9: "Visionary")
In the Delta Quadrant, a network of ancient relay stations claimed by the Hirogen were powered by quantum singularities approximately a centimeter in diameter, putting out four terawatts of energy. (VOY: "Hunters")
Among the known races that utilize Quantum singularities to power their propulsion systems are the Romulans and the Joz, both of which reside in the Beta Quadrant.