In texts about quantum computing, one prepares electrons or other particles in definite spins (up or down), then pass them through various gates, etc. But since the probability that an electron changes spin state within a very short time, then how can this be realistically done? Is there a way to keep the electron in a fixed state long enough? Or does one simply create a lot of particles and assume that statistically a certain percentage will be in the desired state? Am I just stating the problem called decoherence?