Quantum decoherence and measurement

[thegreenlaser]

I keep hearing about things like "quantum decoherence" and the notion that measurement doesn't need a conscious observer. However, I haven't really seen these topics discussed in any of the textbooks I've used (mostly on the level of Griffiths and higher). I haven't even seen a reference to "quantum decoherence" in a textbook, and measurement discussions don't usually seem to talk about what counts as a measurement in practise. Rather, they tend to focus on what happens when a measurement is performed. I don't know if the two concepts are even related, but where can I learn about this sort of thing? I'm guessing maybe Ballentine for the "what counts as a measurement" question, but he doesn't appear to cover decoherence.

Edit: I should probably clarify, since it might seem like I'm asking for an answer to the measurement problem. I realize the measurement problem isn't really resolved, but I frequently hear people saying confidently that (at least in practise) unconscious "observers" are able to perform measurements. I'm wondering if these people are wrong, or if they've learned something that I haven't.

 

[ShayanJ]

This book is a nice introduction.

 

[George Jones]

For a somewhat contrarian take on decoherence, see Weinberg in his grad-level text "Lectures on Quantum Mechanics",

https://www.amazon.com/dp/1107028728/?tag=pfamazon01-20

There seems to be a widespread impression that decoherence solves all obstacles to the class of interpretations of quantum mechanics which take seriously the dynamical assumptions of quantum mechanics as applied to everything, including measurement. My own opinion is that these interpretations, like the Copenhagen interpretation, remain unsatisfactory. ...

Statements of this sort about probabilities are predictions about how the state vectors evolve in time during measurements, so if measurement is really described by quantum mechanics, then we ought to be able to derive such formulas by applying the time-dependent Schrodinger equation to the case of repeated measurement. This not just a matter of intellectual tidiness, of wanting to reduce the postulates of physical theory to the minimum number needed. If the Born rule cannot be derived the time-dependent Schrodinger equation, then something else is needed, something outside the scope of quantum mechanics, and the many worlds interpretation thus shares the inadequacies of the Copenhagen interpretation. ...

 

[atyy]

Edit: I should probably clarify, since it might seem like I'm asking for an answer to the measurement problem. I realize the measurement problem isn't really resolved, but I frequently hear people saying confidently that (at least in practise) unconscious "observers" are able to perform measurements. I'm wondering if these people are wrong, or if they've learned something that I haven't.

There are two flavours of this sort of claim.

The first sort is traditional, and does not claim to solve the measurement problem. An example of this is found in Landau and LIfshitz's quantum mechanics textbook. They say that a classical measurement apparatus interacting with the quantum system makes a measurement. However, they still need someone to make the classical/quantum cut, and they note that there is a measurement problem - in their words - classical mechanics is not a less fundamental theory than quantum theory, because classical mechanics is needed to formulate quantum theory.

The second sort is new and mistaken (eg. Anderson, whose claim is described in http://arxiv.org/abs/quant-ph/0112095), or makes the claim within
(1) some version of Many-Worlds, in conjunction with the proposed derivation of the Born rule for Many-Worlds by Deutsch, and elaborated on by Wallace. Whether this is correct is still debated
(2) Bohmian mechanics, which is generally regarded as ok for non-relativistic quantum mechanics, but the extension to relativistic quantum mechanics is still being researched.

http://arxiv.org/abs/quant-ph/0209123
Do we really understand quantum mechanics?
Franck Laloe

http://arxiv.org/abs/0712.0149
The Quantum Measurement Problem: State of Play
David Wallace