Main Question or Discussion Point
I read about how a quantum computer would work, but how close are we to making one. If it isn't possible what would prevent it from being created?
It is short, but is not THAT short. The coherence times of e.g. atomic/ionic spin systems can be quite long (ms or longer) but the problem is that it is very difficult to scale such systems up to practical computers. Another problem is the time it takes to perform a gate operations is relatively long (remember that it is not only the coherence time that counts, it is how many operations you can perform during that time)The decoherence time of a quantum state in a qubit is short, say 1ps-1fs. After that time the memory is destroyed, any you cannot read.