Graduate student proves a quantum uncertainty principle for fractals

Posted by bookofjoe 3 hours ago

Graduate student proves a quantum uncertainty principle for fractals(www.quantamagazine.org)

37 points | 5 comments

akkartik 1 hour ago|

"In 2017, Dyatlov and Long Jin from Tsinghua University in Beijing used the one-dimensional fractal uncertainty principle to prove that you can never trap a wave on a hyperbolic surface; it will always spread out until it touches every corner. To do so, they imagined a region on the surface that a wave never enters, even after having infinite time to spread out. When they removed all the trajectories that entered that region, what remained was the same sort of fractal dust that appeared in the pinball example. Since the fractal uncertainty principle forbids a wave from being trapped on a fractal, no such region can exist — the wave must spread everywhere."

As a non-mathematician this is a wonderfully evocative summary. I'm curious if mathematicians find it a reasonable characterization of the proof.

linuxhansl 1 hour ago|

As a physics layman I find it fascinating how quantum mechanics are tied to information theory.

For example, take quantum decoherence (which, IMHO, is the most logical explanation for the collapse of the wave-function - by saying it does not actually collapse). Quantum decoherence is almost like a giant constraint resolution system - once a particle randomly interacts with another they become entangled and both now have fewer degrees of freedom. When it interacts with many particles, like any macro-effect it has essentially no degrees of freedom anymore. It's all about who knew about what and when. The experiments around this fascinating. (Note that there are other theories, like the many-worlds interpretation, that also explain the collapse of the wave function)

This seems to be another example of this. Anyway, as I said, just a layman.

tauwauwau 1 hour ago|

Doesn't entanglement mean that entangled particles just cannot have same state of the entangled quantum property at the same time, but they can still achieve all states, essentially preserving their degrees of freedom

drdeca 1 hour ago||

No.

A state is entangled when it isn’t a product state.

Two spin (1/2) particles in a singlet state have the kind of “they have opposite states” thing going on that you describe, and is a specific way that two particles can be entangled.

tauwauwau 1 hour ago||

OK, so instead of having all states (00, 01, 10, 11) available in entangled state they only have 01 and 10 available because they have to be opposite of each other, but even with that these particles individually are able to have both states right? I'm not knowledgeable in this field, I just have interest.