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ZENODO
Preprint . 2023
License: CC BY
Data sources: ZENODO
ZENODO
Preprint . 2023
License: CC BY
Data sources: Datacite
ZENODO
Preprint . 2023
License: CC BY
Data sources: Datacite
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Von Neumann Entropy and Nonorthogonal States

Authors: Ruggeri, Francesco R.;

Von Neumann Entropy and Nonorthogonal States

Abstract

The von Neumann entropy: Trace( -density ln(density)), which is applied to a set of quantum mechanical states, is similar in form to Shannon's entropy, - Sum over i P(i) ln(P(i)). In fact, the two are equal if the density matrix is diagonal with P(i) as the eigenvalues and Sum over i P(i)=1. In the literature (1), it is noted that the value of the von Neumann entropy may change if one uses different basis states. This is considered a problem. If the states are created using an unitary operator acting on an original orthonormal set, then (2) shows that the von Neumann entropy is unchanged. In general (1), however, this is not the case. (1) suggests that one should find the set of states which yield the lowest Shannon entropy. We try to argue that the origins of the form: P(i) ln(P(i)) in classical statistical mechanics follow from the independence of probabilities and the nonoverlap of their states and try to extend this idea to quantum states. For a set of states which yield a diagonal density matrix, unitary transformations yield a set of basis states which are still orthonormal, i.e. independent. If one uses states which are not orthogonal as a basis, the states are no longer independent even though one still has a set of P(i) which sum to 1. We consider a 2 state orthogonal system (eigenfunctions of a Hamiltonian) and simultaneously of an operator A (i.e [H.A]=0). We define density operators as: d = Sum over i p(i) I i> be the same regardless of the basis used. In the two-state case, this may lead to different von Neumann entropy values for states which are not created by a unitary transform of the inital two energy eigenstates. We argue that the p(1)=p(2) = .5 eigenstate represents an extremization of entropy and that a shift to nonorthogonal states leads to a higher negative entropy. We also argue that nonorthogonal states have an overlap and so are not independent whereas physically the probabilities used classically are assocated with states which do not overlap, i.e. a heads up or down coin represent nonoverlapping states.

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selected citations
These citations are derived from selected sources.
This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
BIP!Impulse provided by BIP!
0
Average
Average
Average