I may have been wrong about the picojoule problem. Optalysys claims they have a computer which uses orders of magnitude less power than conventional transistors. Their optical switching technology may be just what we need to keep the Top500 on track to achieve machine level intelligence by 2040 without the need of dedicated nuclear power plants.

Here is a press release and other excerpts from their website:

Using diffraction and Fourier Optics, coupled with our novel designs, we are able to combine matrix multiplication and Optical Fourier transforms into more complex mathematical processes, such as derivative operations. In place of lenses, we also use liquid crystal patterns to focus the light as it travels through the system. This means the tight alignment tolerances that exist through the system are achieved through the dynamic addressing in the software.

All the components used in the Optalysys systems will be low voltage driven, allowing large processing tasks to be carried at a fraction of the running cost of a large processor array or supercomputer. The current largest supercomputer Tianhe-2, reportedly consumes 24MegaWatts of power at peak performance and costs millions of dollars per year to run. In comparison the Optalysys systems will run from a standard mains power supply.