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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
by linuxhansl 1mo 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 1mo agoDoesn'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 1mo agoNo. 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 1mo agoOK, 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.
- fasterik 1mo ago00, 01, 10, 11 are separable states, meaning that a pair of particles in one of those states can be described as two separate one-particle systems. For example, 01 means that the first particle is in the state 0 and the second particle is is in the state 1. A state like (01 + 10) is not separable, so by definition it's an entangled state. "Separability" is a straightforward algebraic fact that follows from the definition of a vector and the tensor product. You can see what this means in the following Google answer https://share.google/aimode/13jNpR7bmpPMo1pn3 https://share.google/aimode/13jNpR7bmpPMo1pn3 (01 + 10) means that if I measure the first particle and get 0, then the second particle is now in the state 1. If I measure the first particle and get 1, then the second particle is now in the state 0.
- drdeca 1mo agoThe state you describe, sqrt(1/2) ( |01> + |10>) is an entangled state, but not all entangled states are like that. The state sqrt(1/2) ( |00> + |11> ) is also possible, and is also an entangled state, but doesn’t have the two particles in opposite states. By contrast, the state (1/2) (|00> - |01> + |10> - |11>) is (while a valid state) not an entangled state, because it is equal to (1/2) (|0> + |1>) (|0> - |1>) .
- marginalia_nu 1mo agoIf quantum probability is a wave function, and interaction introduces a phase shift, this alone is enough to lead to decoherence through the same mechanics as classical optical (de)coherence. In the same circumstances a light beam stops producing an interference pattern in the Young experiment, quantum wave functions do as well. This is pretty easy to derive, just introduce a random phase shift term, and average across it, and the interference pattern disappears and a bell curve emerges instead.