Like in the CERN lab effort, the smaller you digging into understand subparticles, the larger the forces required (The practical size of a magnetic field generator is not limited by the size but the COST and complexity of the structure).
Likewise, I infer by your comment Max, that there is a practical limit of economics.
The cool factor can only take you so far.
Very strange how history repeats itself. The Turing machine is Alan Turing's mathematical proof that a programmable digital computer was possible using nothing but George Bool's logic gates, however they had to wait for Tommy Flowers to invent a working vacuum tube logic gate. In 1985, David Deutsch described a quantum Turing machine using nothing but Richard Feynman's Qbits, or in other words a mathematical proof that a programmable quantum computer was possible. Now we are waiting on someone to invent a practical quantum logic gate. Just recently, a single atom transistor has been created (http://www.purdue.edu/newsroom/research/2012/120219KlimeckAtom.html). I wonder when this article will be repeated for the, as yet to be created, quantum Turing machine.