Comment Not the right article (Score 1) 418
Doesn't anyone read the articles? It says that the article in Phys. Rev. Lett. was published _today_, October 13, 2009. The article that was linked to is two years old and not really relevant.
This is the one they're talking about: http://link.aps.org/doi/10.1103/PhysRevLett.103.160502
There's a preprint at: http://arxiv.org/abs/0905.3417
The gist of it is that one can consider a fundamental step of a computation to be the evolution of a quantum system from a state to an orthogonal state (cause if they aren't orthogonal, you're going to get the answer wrong). They figure out the maximum rate at which the system can evolve between orthogonal states, which sets a maximum to the speed of the computation.
Turns out that the rate is proportional to the difference in energy of the two states -- which means that you can drive the computation faster by choosing two states that have very different energies. But if you do that, since you need to have a power source driving the system between the two energy levels, you have to spend a lot of energy to keep the rate up.
Sort of obvious, but they work out the details with explicit lower bounds for the first time