The smallest transistor is bounded by the atomic radius; a recent paper boasts 0.34nm for a graphene transistor. Scaling that up, to borrow a phrase from quant

The smallest transistor is bounded by the atomic radius; a recent paper boasts 0.34nm for a graphene transistor. Scaling that up, to borrow a phrase from quantum computing, is "just an engineering problem." But for now we can only produce things on the atomic scale a handful of atoms at a time, and making a trillion-transistor processor would take somewhere between thousands and billions of years with today's tech.