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Title: Unital quantum operations on the Bloch ball and Bloch region

Journal Article · · Physical Review. A
;  [1]
  1. Department of Mathematics, Washington and Lee University, Lexington, Virginia 24450 (United States)

For one-qubit systems, we present a short, elementary argument characterizing unital quantum operators in terms of their action on Bloch vectors. We then show how our approach generalizes to multiqubit systems, obtaining inequalities that govern when a 'diagonal' superoperator on the Bloch region is a quantum operator. These inequalities are the n-qubit analog of the Algoet-Fujiwara conditions. Our work is facilitated by an analysis of operator-sum decompositions in which negative summands are allowed.

OSTI ID:
20640706
Journal Information:
Physical Review. A, Vol. 69, Issue 2; Other Information: DOI: 10.1103/PhysRevA.69.022314; (c) 2004 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 1050-2947
Country of Publication:
United States
Language:
English