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Suppose you have a standard spin qubit: spin "up" is $|1\rangle$ and spin "down" is $|0\rangle$ . Your qubit is in some storage location which does not couple the two spin directions to each other or have any different energy, you store $|\psi\rangle = a |0\rangle + b |1\rangle$ in this qubit. ` Now some proton flies by, or a minor fluctuation in the Earth's ...

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It is not the out of phase states that get dissipated to wider environment. Rather, it is only the interference components with those out of phase states that get dissipated into the wider environment. I know you got to this question from a question about the Everett ("many worlds") interpretation. If you find Timaeus' more technical description difficult ...

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The article isn't bad, but the author rather presents hypothesis as fact. For example look at this bit: If a particle interacts with just a single photon, for example, then the two particles will enter an entangled state and that will be enough to trigger the onset of decoherence (for example a single photon entering the double-slit experiment will be ...

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A density matrix quantum mechanically is a way to easily model the many body wave function of a many particle system. It is a matrix whose off diagonal elements keep the phases between the disparate wavefunctions and the amplitude of projecting particle A to particle N. This is the "information" that particle A has for the existence of particle N. Thus ...

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Right before the part you boldfaced and right after the part you didn't boldface there was a parenthetical part. And the parenthetical included a link. In the link the author is pretty clear that the phases are in the reduced density matrix. A reduced density matrix is about reproducing the statistics and usually about adding some classical statistics on ...

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In non relativistic quantum mechanics you have a partial differential equation like the Schrödinger equation. The solutions are called wavefunctions. It is similar to Maxwell's equations in that if you provide the values at one time you can get the values at a later time. Unlike Maxwell the values you need to provide are complex and unlike Maxwell you need ...

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