- quantum: The smallest quantity of radiant energy, equal to Planck's constant times the frequency of the associated radiation. (plural: quanta). 
Quantum is a shorthand term. While it's convenient, conceptually speaking, to think of "Quantum energy," such a thing doesn't really exist. In actuality, a nova manipulates some combination of the four fundamental forces: the strong nuclear force, the weak nuclear force, the electromagnetic force, and gravity.
As these four forces are responsible for nearly all observed physical phenomena, being able to manipulate these four forces means a nova (or quantakinetic, for that matter) is theoretically capable of doing anything, limited only by their own psyche.
Quantum isn't the only element which makes up the universe, however. The "fifth force," psi, governs information and (perhaps) consciousness itself. It is the final element in a true grand unification theory. Together, quantum energy and psi have been called "telluric energy."
Oddly enough, the manipulation of quantum appears to be unique to humanity, whether acheived directly (the M-R node) or via the secondary medium of psi (quantakinesis). This is most likely the main reason the Doyen fear humans to the degree that they do, as quantum is one of the few things that can actually harm them directly.