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A characterization of freeness by invariance under quantum spreading

  • Stephen Curran EMAIL logo
Published/Copyright: April 14, 2011
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Journal für die reine und angewandte Mathematik
From the journal Volume 2011 Issue 659

Abstract

We construct spaces of quantum increasing sequences, which give quantum families of maps in the sense of Sołtan. We then introduce a notion of quantum spreadability for a sequence of noncommutative random variables, by requiring their joint distribution to be invariant under taking quantum subsequences. Our main result is a free analogue of a theorem of Ryll–Nardzewski: for an infinite sequence of noncommutative random variables, quantum spreadability is equivalent to free independence and identical distribution with respect to a conditional expectation.

Received: 2010-02-23
Revised: 2010-06-08
Published Online: 2011-04-14
Published in Print: 2011-October

© Walter de Gruyter Berlin · New York 2011

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