Selective molecular polarization is a process whereby a substance can be altered to produce a certain form of energy.
Such a procedure was performed by the Devidians, in a cavern on their home planet in the 24th century. By subjecting the rock face to selective molecular polarization, they were able to modify it to produce triolic waves, which they used to focus minute distortions in the space-time continuum produced by an ophidian-like creature in their possession into a temporal vortex. They performed the same procedure in a cavern under the Presidio in San Francisco in 1893, allowing them to travel back and forth through time between the two locations. (TNG: "Time's Arrow", "Time's Arrow, Part II")