A quantum theorist was a scientist who theoretically dealt with quantum mechanics. After failing to remove interspatial parasites from Jonathan Archer, Doctor Phlox returned to Denobula to consult with some of the finest quantum theorists and neurosurgeons. (ENT: "Twilight") Kent State University quantum theorists were able to duplicate a single particle of matter using a spatial scission. Kathryn Janeway's duplicate mentioned this in 2372 when speculating how the duplication could have occurred. (VOY: "Deadlock")