Timeline for Are superpositions contagious?
Current License: CC BY-SA 4.0
6 events
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| Oct 3, 2022 at 14:23 | comment | added | FlatterMann | Weak measurement/decoherence for the transition from quantum mechanics to classical physics has been suggested by Heisenberg in 1927, I believe, and by Mott in 1929. Zurek was certainly not the first person to think about it. If anything, he was very late. | |
| Jul 17, 2019 at 16:24 | comment | added | oleg | You are correct to suspect pointer states as some arbitrarily selected degrees of freedom that happen to do the job. The resolution of that has to do with the nature of interaction of the macroscopic system with its environment. The pointer basis are not chosen by us, they are selected by which degrees of freedom interact with the environment and how. This information is again encoded in the Hamiltonian. Since we cannot control this Hamiltonian completely we cannot measure whatever we want. It is not easy to see how it works without carefully following the math (look up einselection). | |
| Jul 17, 2019 at 16:14 | comment | added | oleg | Entanglement is a consequence of interaction. In general we describe dynamics with Hamiltonians which specify both how the individual systems evolve (self part of the Hamiltonian) and how their mutual states evolve together (interaction part). A measurement device is described by a Hamiltonian with tunable interaction part (usually some kind of EM field) that the experimenter turns on briefly (pulse) to generate time evolution that correlates (entangles) some degree of freedom of the apparatus (like polarization of atoms) with the measured system. You should look up concrete examples. | |
| Jul 17, 2019 at 6:19 | comment | added | Andrei | cont: If we split a diatomic molecule with 0 angular momentum we get entangled atoms. We know that on any axis the sum of their spins must be 0. By this logic we can also say that when a particle interacts with an instrument the total angular momentum (particle + instrument) must stay the same, so the particle is entangled with the instrument. But clearly, the angular momentum of the instrument and the position of the pointer are different things. So how can you arrive at the conclusion that you get entanglement between particle states and pointer states? | |
| Jul 17, 2019 at 6:12 | comment | added | Andrei | oleg, thanks for your detailed answer! I understand to some extent the measurement problem and the attempted solution be decoherence. But my first issue starts with the assumptions that 1. px (pointer states) are indeed proper quantum states spanning a corresponding Hilbert space and 2. we get an entanglement between the particle and the pointer. To my limited knowledge, entanglement is a consequence of conservation principles + uncertainty about the subsystems. -to continue | |
| Jul 16, 2019 at 16:43 | history | answered | oleg | CC BY-SA 4.0 |