Does a real macroscopic body, like table, human or a cup permits description as

Question

Does a real macroscopic body, like table, human or a cup permits description as a wave function? When is it possible and when not?

For example in the "Statistical Physics, Part I" by Landau & Lifshitz it is argued that such systems must be described via the density matrix (chapter I, about statistical matrix). As far as I got it, roughly speaking, macroscopic bodies are so sensible to external interaction that they never can be counted as systems, one have to include everything else to form a system. Is my interpretation right?

When is it wrong to talk about wave functions of bodies that surround us?

Explanation / Answer

Those degrees of freedom of a quantum system that are described by a pure partial state must be very well shielded from unwanted interactions with the environment, otherwise they will be decoherered to a mixed state in a moment. This shielding can be done for a few degrees of freedom (like a superconducting current) but not for position and momentum of macroscopic bodies. Therefore these dof are always described by density matrices.

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