A matrix representation of the ► state operator. So named because in the position basis its diagonal elements are equal to the position probability density. This name is older than the modern term state operator, and is still frequently used in its place, especially in many-electron theory and ► quantum chemistry. The name density matrix is not entirely accurate, since in the position basis it is not really a matrix, but rather a function of two continuous variables. If a discrete basis is chosen (such as the spin basis), then it becomes a genuine matrix, but its diagonal elements are probabilities rather than densities. ► States, pure and mixed, and their representation.
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© 2009 Springer-Verlag Berlin Heidelberg
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Ballentine, L. (2009). Density Matrix. In: Greenberger, D., Hentschel, K., Weinert, F. (eds) Compendium of Quantum Physics. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-540-70626-7_51
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DOI: https://doi.org/10.1007/978-3-540-70626-7_51
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