Communications in Mathematical Physics

, Volume 303, Issue 2, pp 555–594 | Cite as

Factorization and Dilation Problems for Completely Positive Maps on von Neumann Algebras

  • Uffe Haagerup
  • Magdalena MusatEmail author


We study factorization and dilation properties of Markov maps between von Neumann algebras equipped with normal faithful states, i.e., completely positive unital maps which preserve the given states and also intertwine their automorphism groups. The starting point for our investigation has been the question of existence of non-factorizable Markov maps, as formulated by C. Anantharaman-Delaroche. We provide simple examples of non-factorizable Markov maps on \({M_n(\mathbb{C})}\) for all n ≥ 3, as well as an example of a one-parameter semigroup (T(t)) t≥0 of Markov maps on \({M_4(\mathbb{C})}\) such that T(t) fails to be factorizable for all small values of t > 0. As applications, we solve in the negative an open problem in quantum information theory concerning an asymptotic version of the quantum Birkhoff conjecture, as well as we sharpen the existing lower bound estimate for the best constant in the noncommutative little Grothendieck inequality.


Tracial State Embedding Problem Normal Faithful State Noncommutative Setting Asymptotic Quantum 
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© Springer-Verlag 2011

Authors and Affiliations

  1. 1.Department of Mathematical SciencesUniversity of CopenhagenCopenhagen ØDenmark

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