> Il 4 dicembre 2018 alle 16.36 [email protected] ha scritto: > > > > On Tuesday, December 4, 2018 at 10:13:38 AM UTC, Bruno Marchal wrote: > > > > > > > > > > > On 3 Dec 2018, at 20:57, [email protected] > > wrote: > > > > > > > > > > > > On Sunday, November 18, 2018 at 1:05:26 PM UTC, > > > agrays...@http://gmail.com wrote: > > > > > > > > > > > > > > > > > > On Saturday, November 17, 2018 at 7:39:14 PM UTC, > > > > [email protected] wrote: > > > > > > > > > > > > > If you write a > > > > superposition as a sum of eigenstates, why is it important, or > > > > relevant, or even true that the component states are coherent since > > > > eigenstates with distinct eigenvalues are orthogonal. This means there > > > > is no interference between the components of the superposition. AG > > > > > > > > > > > > > > > > > > Put another way; from what I've read, coherence among > > > > components of a superposition is necessary to guarantee interference, > > > > but since an eigenstate expansion of the superposition consists of > > > > orthogonal, non interfering eigenstates, the requirement of coherence > > > > seems unnecessary. AG > > > > > > > > > > > > > > For decoherence to occur, one needs, presumably, a coherent > > > superposition. But when the wf is expressed as a sum of eigenstates with > > > unique eigenvalues, those eigenstates are mutually orthogonal; hence, > > > IIUC, there is no coherence. So, how can decoherence occur when the state > > > function, expressed as a sum of eigenstates with unique eigenvalues, is > > > not coherent? I must be missing something, but what it is I have no clue. > > > AG > > > > > > > > > > > > > > Decoherence never occurs, except in the mind or memory of the > > observer. Take the state up + down (assuming a factor 1/sqrt(2)). And O is > > an observer (its quantum state). > > > > > > > > > > O has the choice to measure in the base {up, down}, in which case > > the Born rule says that he will see up, or down with a probability 1/2. He > > will *believe* that decoherence has occurred, but if we long at the > > evolution of the whole system O + the particle, all we get is > > > > O-up up + O-down down, > > > > And some other observer could in principle test this. (O-up means O > > with the memory of having seen the particle in the up position). > > > > But O could measure that particle in the base {up+down, up-down). > > He has just to rotate a little bit its polariser or Stern-Gerlach device. > > In that case he obtains up+down with the probability one, which souls not > > be the case with a mixture of up and down. In that case, coherence of up > > and down do not disappear, even from the pot of the observer. > > > > Decoherence is just the contagion of the superposition to anything > > interacting with it, including the observer, and if we wait long enough the > > whole causal cone of the observer. > > > > Bruno > > > > > > Thanks, but I'm looking for a solution within the context of interference > and coherence, without introducing your theory of consciousness. Mainstream > thinking today is that decoherence does occur, but this seems to imply > preexisting coherence, and therefore interference among the component states > of a superposition. If the superposition is expressed using eigenfunctions, > which are mutually orthogonal -- implying no mutual interference -- how is > decoherence possible, insofar as coherence, IIUC, doesn't exist using this > basis? AG >
There are instruments like the MZI (Mach-Zehnder Interferometer).. In this insrtrument one (spli)amplitude goes through path A, the other (plit)amplitude goes through par'th B. At the end of their travef both amplitudes recombine interferentially giving *always a single* outome. As for the de-coherence frankly i did not realize its conceptual meaning. > > > > > > > > > -- You received this message because you are > > subscribed to the Google Groups "Everything List" group. > > > To unsubscribe from this group and stop receiving emails from > > > it, send an email to [email protected]. > > > To post to this group, send email to > > > [email protected]. > > > Visit this group at > > > https://groups.google.com/group/everything-list > > > https://groups.google.com/group/everything-list . > > > For more options, visit https://groups.google.com/d/optout > > > https://groups.google.com/d/optout . > > > > > > > > > > > > > > > > -- > You received this message because you are subscribed to the Google Groups > "Everything List" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected] > mailto:[email protected] . > To post to this group, send email to [email protected] > mailto:[email protected] . > Visit this group at https://groups.google.com/group/everything-list. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
