Fractions are under any modulus are actually representable as whole numbers (provided they don’t share factors with the modulus).

For example under mod 21 a half can actually be represented by 11. Try it. Times any even number by 11 and you’ll see you halved it.

Take any number that’s a multiple of 4 and times it by 16 under mod 21. You now have that number divided by 4.

Etc.

Absolutely nothing to do with quantum computers.