Technically, it's not a laser, but something called spaser. Instead of photons, it uses plasmons, a particle only 44 nanometres across. It could push CPUs' speeds to hundreds of terahertz, according to Mark Stockman, professor of physics at Georgia State.
The spaser works about a thousand times faster than the fastest transistor, while having the same nanoscale size. This opens up the possibility to build ultrafast amplifiers, logic elements, and microprocessors working about a thousand times faster than conventional silicon-based microprocessors.
This new method treats light in a different way than traditional optical CPUs, which are "difficult to miniaturise because you can't contain photons in areas smaller than half their wavelength". In other words: Optical CPUs won't fit in current electronics. Plasmonic devices, on the other side, can concentrate these nanoparticles in spaces similar to current processors. [Technology Review]