In the SEP, on its discussion of ancient theories of the soul, they say:
Epicurus is an atomist, and in accordance with his atomism he takes the soul, like everything else that there is except for the void, to be ultimately composed of atoms.
Our sources are somewhat unclear as to exactly which kinds of materials he took to be involved in the composition of soul. It is very probable, though, that in addition to some relatively familiar materials — such as fire-like and wind-like stuffs, or rather the atoms making up such stuffs — the soul, on Epicurus' view, also includes, in fact as a key ingredient, atoms of a nameless kind of substance, which is responsible for sense-perception.
Thus it seems that while he thought he could explain phenomena such as the heat or warmth of a living organism, as well as its movement and rest, by appealing to relatively familiar materials and their relatively familiar properties, he did feel the need to introduce a mysterious additional kind of substance so as to be able to explain sense-perception, apparently on the grounds that “sense-perception is found in none of the named elements”
Qualia seems to have a roughly similar semantic range. That is qualia is the embodied perception and not its theoretical cognate. For example the purple of a purple grape has a particular wavelength of light. But it isn't this we perceive - we perceive purple.
One can say, pace Epicurus, Qualia is not found in matter.
Why does Epicrus not say, as would seem the simplest move, to say that Qualia is found in the mind?
Is this because, as the SEP implies, that to understand Qualia is to understand mind?