Quantum level
From Memory Alpha, the free Star Trek reference.
The quantum level is a term used for activity that takes place on a sub-atomic scale. This quantum scale is so small, compared to normal physical bodies, that Earth scientists didn't discover it until centuries of developing physics and technology.
As a measure for the difference between normal and quantum scale, Planck's constant is sometimes quoted.
In 2370, Commander Data attempted to explain to Lieutenant Worf the theory of quantum levels when he discovered that Worf had traveled to various different quantum universes. (TNG: "Parallels")
