Defeating Heisenberg's Uncertainty Principle

eldavojohn writes "As we strive closer and closer to quantum computing, physics may need to be improved. A paper released in Nature Physics suggests that the limit defined by Heisenberg's Uncertainty Principle can be beaten with quantum memory. From the article, 'The cadre of scientists behind the current paper realized that, by using the process of entanglement, it would be possible to essentially use two particles to figure out the complete state of one. They might even be able to measure incompatible variables like position and momentum. The measurements might not be perfectly precise, but the process could allow them to beat the limit of the uncertainty principle.' Will we find out that Heisenberg was shortsighted in limiting the power of quantum physics or will the scientists be surprised to find that such a theoretical scenario — once conducted — performs unexpectedly in Heisenberg's favor?"

Comments

Bad choice of names?

[Krokant]

For those interested, the preprint of the Nature article can be found at: http://arxiv.org/abs/0909.0950

However, I don't really see what the fuzz is about. What they are in fact demonstrating is a relationship between conditional von Neumann entropies, which they claim is a measure of "uncertainty" (it is in a specific meaning of the word "uncertainty"). However, there is a difference between von Neumann entropy and the variance of a physical observable as used in the Heisenberg uncertainty principle. On the other hand, if you label a physical property such as entropy "uncertainty" and demonstrate a relationship between those entropies, then you can indeed call that an "uncertainty relation" but that's just a cheap way of attracting attention.

Also, I am not sure if it is possible to obtain the Heisenberg uncertainty relation from their equation. I would expect that, for example by entering pure, disentangled states in their equation, that Heisenberg should be recoverable (because of course, Heisenberg also applies to pure states). I don't immediately see how that can happen since the von Neumann entropy for a pure state is zero. Perhaps I am just missing something and perhaps my QM is a bit rusty :).