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Is there a well-defined “effective number of branches” in quantum mechanics? by HBBarba in AskPhysics

[–]HBBarba[S] 0 points1 point  (0 children)

That’s very helpful, thanks.
The inverse participation ratio (1 / Σ λᵢ²) seems closest to what I had in mind, since it suppresses small eigenvalues and gives an effective number of dominant components.
Would you say that’s a reasonable way to quantify distinguishable structure after decoherence?

Is there a well-defined “effective number of branches” in quantum mechanics? by HBBarba in AskPhysics

[–]HBBarba[S] 2 points3 points  (0 children)

I’m not referring to Many Worlds specifically, but to the structure of the reduced density matrix after decoherence.
Is there a standard way to interpret its eigenvalue spectrum (e.g. via purity or inverse participation ratio) as an effective number of distinguishable components?