WordNet records no synonym and no antonym for quantum. It is the only member of each of its synsets, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
a discrete amount of something that is analogous to the quantities in quantum theory
(physics) the smallest discrete quantity of some physical property that a system can possess (according to quantum theory)
Synonyms, antonyms and the broader and narrower relations for quantum come from Princeton University’s WordNet. Full sources and licences.