New York Journal of Mathematics
Volume 28 (2022), 580-609


Sarah Plosker and Christopher Ramsey

Bistochastic operators and quantum random variables

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Published: March 9, 2022.
Keywords: positive operator valued measure (POVM), quantum probability measure, quantum random variable, Radon-Nikodým derivative, Bistochastic operator, majorization.
Subject: 46B22, 46C50, 46G10, 47G10, 81P15.

Given a positive operator-valued measure ν acting on the Borel sets of a locally compact Hausdorff space X, with outcomes in the algebra B(H) of all bounded operators on a (possibly infinite-dimensional) Hilbert space H, one can consider ν-integrable functions X → B(H) that are positive quantum random variables. We define a seminorm on the span of such functions which in the quotient leads to a Banach space. We consider bistochastic operators acting on this space and majorization of quantum random variables is then defined with respect to these operators. As in classical majorization theory, we relate majorization in this context to an inequality involving all possible convex functions of a certain type. Unlike the classical setting, continuity and convergence issues arise throughout the work.


S.P. was supported by NSERC Discovery Grant number 1174582, the Canada Foundation for Innovation (CFI) grant number 35711, and the Canada Research Chairs (CRC) Program grant number 231250. C.R. was supported by NSERC Discovery Grant 2019-05430.

Author information

Sarah Plosker:
Department of Mathematics and Computer Science
Brandon University
Brandon, MB R7A 6A9, Canada


Christopher Ramsey:
Department of Mathematics and Computer Science
Brandon University
Brandon, MB R7A 6A9, Canada, and
Department of Mathematics and Statistics
MacEwan University
Edmonton, AB T5J 4S2, Canada