They've taken Moore's Law to the limit. Atoms now then the particles that make the atom them the ones that make the particles. You can't get any smaller than quarks.
Well, I highly doubt that transistors will ever be made out of just quarks. Quarks are inseperable at any kind of rational energy level. which would make it costly. Also, making one out of sub-atomic particles is also unlikely. To make a semi-conductor, you need to have part of the thing conducting and part non-conducting, and the ability to switch between the 2. This is reliant on having multiple particles grouped tightly together to give such dynamics. The only way I can see that going down is an atom, but there might be artificially constructed atoms built to work in a specific way.
As for quantum computing... well, for those that dont know, the general idea was that since a quantum system is so difficult to figure out, the thought goes that if you could then control a quantum system, in a particular way, it would be equivelent to carrying out a difficult calculation.
Next, we'll start seeing 'spintronics'. The idea here is that not only does an electron carry a charge to the processor (or wherever it's going), but it also has a spin (this is a strange use of the word and is difficult to understand. just think of it as a category for now). A particular kind of spin is labeled '1' and another '0'. So now, each electron carries twice the information it did before.
So, basically, we start to control more and more of what we already have in the system and use it to carry more information. eventually some of the weird quantum affects will be present in the system and will also be used to compute things better. this is when we will have a quantum computer.