The way I am coming to understand it, the allowed states that an observable can be "observed/measured" in are defined by the eigenvectors (and associated eigenvalues) of the observable's operator. Since those eigenvectors form a basis and span the space of vectors defined by the operator, a linear combination of two or more eigenstates is also an allowed state of the observable i.e. superposition.(adsbygoogle = window.adsbygoogle || []).push({});

Does this mean that an observablecan beobserved/measuredin a state which is a superposition of eigenstates?

Here is a quote from Dirac's book "The Principles of Quantum Mechanics". I do not have this book and I have not read this book, yet!) Someone in another thread mentioned it and that started me on a quest. In that quest I found the following quotation from Dirac's book. Here is that quote...

It seems to me that Dirac is saying, "No, we cannot observe/measure the particle in a superposition of states" "...We are observing whether it is polarized parallel or perpendicular to the optic axis. The effect of making this observation is to force the photon entirely into the state of parallel or entirely into the state of perpendicular polarization. It has to make a sudden jump from being partly in each of those two states to being entirely in one or the other of them. Which of the two states it will jump into cannot be predicted, but is governed only by probability laws."

https://www.amazon.com/Principles-Q...e=UTF8&reviewerType=all_reviews&sortBy=recent

Or maybe he is saying that if we want to observe the photon in itssuperposition statewe need a different way to measure it!

What if we did not want to observe whether the photon was polarized in one of onlytwostates? Did we force it into one of those two states by the method we used to measure it?

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# I Are superposition states observable?

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