During the past forty years astounding advances have been made in the manufacture of computers. The number of atoms needed to represent a bit in memory has been decreasing exponentially since 1950. Likewise the number of transistors per chip, clock speed, and energy dissipated per logical operation have all followed their own improving exponential trends. This rate of improvement cannot be sustained much longer, at the current rate in the year 2020 one bit of information will requite only one atom to represent it. The problem is that at that size the behavior of a computer's components will be dominated by the principles of quantum physics. (Williams, Clearwater)
As components shrink to where their behavior will soon be dominated more by quantum physics than classical physics, researchers have begun to investigate the potential of these quantum behaviors for computation. These physical limitations of the classical computer, and the possibility that the quantum computer can perform certain useful tasks more rapidly than any classical computer drive the study of quantum computing.