Astounding advances have been made in the manufacture of computers between 1950 and 1999. 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. Despite these fantastic advances, the manner in which all computers function has been essentially identical: combinations of a few simple logical operations that process some number of operations per unit time. This rate of improvement in transistor size cannot be sustained much longer, at the current rate as of 199 in the year 2020 one bit of information will requite only one atom to represent it. The problem is that at that level of miniaturization the behavior of the components of a computer will become dominated by the principles of quantum physics. (Williams, Clearwater)

With the size of components in classical computers shrinking to where the behavior of the components may soon be dominated more by quantum physics than classical physics researchers have begun investigating the potential of these quantum behaviors for computation. Surprisingly it seems that a computer whose components are able to function in a quantum are more efficient than any classical computer can be.

It is the physical limitations of the classical computer, and the possibilities for the quantum computer to perform certain useful tasks more rapidly than any classical computer which drive the study of quantum computing.