Cambodge said...In the term "quantum leap" the noun is "leap" and the adjective is "quantum" (i.e. the adjective gives description to the noun).
As noted above, the word "quantum" in it's adjective form means:
–adjective
6. sudden and significant: a quantum increase in productivity.
so "a quantum leap" = "a sudden and significant leap"
Notwal, I'll fester in my grubbiness of truth

. Not for me the clean, post-bath untruths.

The term in question (ibid) is "quantium jump" not "quantum". "Quantum leap" means the same thing.
However:-
quan·tum (kw#335;n't#601;m) Pronunciation Key
n. pl. quan·ta (-t#601;)
1. A quantity or amount.
2. A specified portion.
3. Something that can be counted or measured.
4. Physics
1. The smallest amount of a physical quantity that can exist independently, especially a discrete quantity of electromagnetic radiation.
2. This amount of energy regarded as a unit.
adj. Relating to or based upon quantum mechanics.
[Latin, from neuter of quantus, how great; see quantity.]
src: Dictionary of Truth.
also,
1. sudden and significant: a quantum increase in productivity. (erroneous usage.
src: Dictionary of the Great Unwashed )
That says it all. You have selectively chosen from the Dictionary of the Great Unwashed. If enough drongos misunderstand something and repeat it incorrectly often enough it is added to the dictionary so the rest of us have some means of knowing what the grubby mob is on about. In other words its a self referential error, a semantic abomination to be reviled and resisted. Particularly as it is ambiguous.
Perpetuating the error creates a certain affinity between yourself and the first moron who said to himself "Ooooh, quantum leap, that sounds big" and blithely went about misleading the sheep who knew no better.

Are you a ignorant sheep or a deliberate and vile corrupter of language, an agent of Satan sent to sow confusion?