Thanks a lot for your reply Henk.

hi. please read this: 

http://www.extremetech.com/extreme/189155-google-begins-developing-its-own-quantum-computer-chips-to-prepare-for-the-future

You question is one of the most used in this time.

You see it from holistic commercial side. I mean you can start hope in some cases (called Quantum Circuits). They are quite realistic in special cases.

But in general I suppose the Quantum Computer can't be realized in future "as one unified concept".

As actual state is we need special mathematical algorithms (HADAMARD, DEUTSCH, SHOR) to get parallel functioning and a reverse fixing of states of a Quantum Circuit to get that fascinating "parallel computing". In reality many such special physical circuits are found and all claim to be the first "quantum computer".

So my actual state of knowledge is that a unified quantum computer cant be, because we can't rebuilt the physical world of quants and steer them as we need them for our results. We have to create some very special circuits and surround them by our mathematically defined algorithms to get some effects like our particles have in Quantum Mechanics.

Sure is too that not in all cases a Quantum Computer (Quantum Circuit) is better than our classical computer. That special positive advantages are f. i. : factoring of numbers and combined "cryptomysing" of data.    

So there will be a lot to do for algorithmic and mathematics to use quantum circuits for more cases in commercial purposes.