Defeating Heisenberg's Uncertainty Principle 160
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?"
Perhaps I'm wrong on this... (Score:2, Interesting)
... but I thought entanglement meant for properties such as spin and polarisation, not position and momentum? Quite obviously 2 particles can't share the same position so measuring 1 will do you no good in finding out the position of the other but do they share momentum?
Re:Perhaps I'm wrong on this... (Score:3, Interesting)
Generally entangled particles are created at the same place. For example, certain decay processes will fire off two complementary particles in opposite directions, at the same speed, in order to conserve momentum. If you measure the location of one of those particles, you know that the other must be the same distance from the origin point, in the opposite direction, so you know it's position as well.
Re:Perhaps I'm wrong on this... (Score:5, Interesting)
The uncertainty principle originally made statements about what can be known about position and velocity. You cannot measure both position and velocity simultaneously above a certain degree of accuracy. The more accurate your measure of velocity, the less you know about position, and visa versa. Since most purists will hold this up as the true test of any theory wanting to refute the uncertainty principle, the theorists felt the need to suggest that this, theoretically could be invalidated, as well. Hence the mention of momentum.
The fly in the ointment seems to be this part of the theory:
...maximally entangling a particle with a quantum memory, meaning all states and all degrees of freedom in the particle would be tied to all of the quantum memory's states.
I'm not sure how many states and degrees of freedom would be required. The total is infinite for both, but perhaps these can be limited to ranges. Still the size of the quantum memory would be huge, I think. Also, there is the non-trivial trick of entangling the particle's states and degrees of freedom with the quantum memory states...
I don't think Heisenberg will be turning over in his grave very soon...
Replacement vs. Refinement of Theory (Score:3, Interesting)
Physics is not merely an evolutionary process; occasionally, the models are simply wrong, and must be replaced. For example, consider epicycles. For the purpose of calculation, they were adequate, if expensive. However, a simpler and better theory was found, and they were replaced entirely. Unfortunately, history has shown us that most people will bitterly defend the accepted theory, rather than consider possible alternatives.
As Feynman once said, "If I were forced to sum up in one sentence what the Copenhagen interpretation says to me, it would be 'Shut up and calculate!'." Anyone with common sense would consider the currently accepted interpretation of quantum mechanics to be nonsense. Useful nonsense perhaps, but certainly not a suitable description of the world that just needs some refinement.