Physical mechanism for decoherence?

[billy_boy_999]

i know very little quantum mechanics and would appreciate as qualitative a reply as anyone can muster...

what is the physical mechanism for decoherence? decoherence sounds like a solution to quantum 'weirdness' if i understand it correctly...you have to take into account a myriad quantum systems interacting with each other and this somehow jolts the quantum system back into something like a classical behaviour? but what is the mechanism for this jolting into classical mechanics? what physical process cancels out the ambiguity of the wave function?

 

[slyboy]

Systems interact with their environment via Hamiltonians that naturally interact differently with components of the quantum state that are "macroscopically" different. For example, components which have vastly different energy or position, or the dead and alive components of Schroedinger's famous cat. Ususally, we do not have full information or control of the environment, so we must find a way of describing the state of the system without including all the environmental degress of freedom. If we do this, it turns out that all the quantum coherence between macroscopically distinct components of the state becomes washed out by the interactions with the environment. Thus, we are left with a state that looks a lot more like a classical mixture of possibilities than a quantum superposition.

Some would argue that this is all there is to be said about the reduction of quantum mechanics to classical physics for macroscopic systems. They claim that it solves the measurement problem and related paradoxes. However, note that we still have a quantum superposition if we take the entire system, including the environment, into account. Thus, I think that the appropriate way to view decoherence is as a tool to explain the particular branching that occurs in the many-worlds interpretation. However, this interpretation still has other difficulties, such as the meaning of probability, so it is inapropriate to say that decoherence has solved all the difficulties of quantum mechanics at this point.

 

[Doc Al]

Review paper on Decoherence

For anyone interested in decoherence, there is a recent review paper by M. Schlosshauer: Decoherence, the Measurement Problem, and Interpretations of Quantum Mechanics. A preprint is available at http://arxiv.org/abs/quant-ph/0312059.

It was only recently brought to my attention, so I haven't read it yet.

 

[Gunner B]

Here's a paper written by the famous Leonard Susskind as his way of dealing with the probability issue that slyboy brought up.
http://arxiv.org/abs/1105.3796