Minimum variable size if the information are coded in non-binary system

Question

A typical HDD would represent information as either 1 (e.g. spin up) or 0 (e.g. spin down). Let's assume you want to represent the information physically in a hex system with 16 states, and assume this is possible with using some physical form (maybe the same spin).

What is the minimum physical size of a memory element in this new system in units of binary bits? It seems to me that the minimum is 8 bits = 1 byte. Therefore, going from a binary representation to a higher representation will, everything else equal, make the minimum variable size equal 1 byte instead of 1 bit. Is this logic correct?