Phys. Rev. Lett. 103, 160502 (2009)

The processing speed of computer chips has doubled almost every two years for the past 40, as engineers have crammed ever more transistors into smaller circuits. But according to Lev Levitin and Tommaso Toffoli of Boston University in Massachusetts, chips will ultimately hit a roadblock, limited by the minimum time it takes for a particle to flip from one quantum state to another — a fundamental step in any information system.

There are two independent bounds on this minimum time — one based on the average energy of the quantum system, the other based on the uncertainty in the system's energy. In their calculations, Levitin and Toffoli unify the bounds and show there is an absolute limit to the number of operations that can be achieved per second by a computer system of a given energy. Levitin says that, at the current doubling pace, computing speed will reach this limit in about 80 years.