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EXTREMAL MATRIX STATES ON OPERATOR SYSTEMS

  • DOUGLAS R. FARENICK (a1)
    • Published online: 01 June 2000
Abstract

A classical result of Kadison concerning the extension, via the Hahn–Banach theorem, of extremal states on unital self-adjoint linear manifolds (that is, operator systems) in C*-algebras is generalised to the setting of noncommutative convexity, where one has matrix states (that is, unital completely positive linear maps) and matrix convexity. It is shown that if ϕ is a matrix extreme point of the matrix state space of an operator system R in a unital C*-algebra A, then ϕ has a completely positive extension to a matrix extreme point Φ of the matrix state space of A. This result leads to a characterisation of extremal matrix states as pure completely positive maps and to a new proof of a decomposition of C*-extreme points.

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Journal of the London Mathematical Society
  • ISSN: 0024-6107
  • EISSN: 1469-7750
  • URL: /core/journals/journal-of-the-london-mathematical-society
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