scholarly journals Stinespring's construction as an adjunction

2019 ◽  
Vol 1 ◽  
pp. 2
Author(s):  
Arthur J. Parzygnat
Keyword(s):  
Hilbert Space ◽  
Natural Transformation ◽  
Adjoint Action ◽  
Universal Property ◽  
Completely Positive Map ◽  
Completely Positive Maps ◽  
Completely Positive ◽  
Bounded Linear ◽  
Finite Dimensional ◽  
Positive Maps

Given a representation of a unital C∗-algebra A on a Hilbert space H, together with a bounded linear map V:K→H from some other Hilbert space, one obtains a completely positive map on A via restriction using the adjoint action associated to V. We show this restriction forms a natural transformation from a functor of C∗-algebra representations to a functor of completely positive maps. We exhibit Stinespring's construction as a left adjoint of this restriction. Our Stinespring adjunction provides a universal property associated to minimal Stinespring dilations and morphisms of Stinespring dilations. We use these results to prove the purification postulate for all finite-dimensional C∗-algebras.

scholarly journals When do pieces determine the whole? Extreme marginals of a completely positive map

2014 ◽  
Vol 26 (02) ◽  
pp. 1450002 ◽  
Author(s):  
E. Haapasalo ◽  
T. Heinosaari ◽  
J.-P. Pellonpää
Keyword(s):  
Hilbert Space ◽  
Von Neumann Algebras ◽  
Common Source ◽  
Completely Positive Map ◽  
Bounded Operators ◽  
Completely Positive Maps ◽  
Completely Positive ◽  
Von Neumann ◽  
Positive Maps ◽  
The Common

We will consider completely positive maps defined on tensor products of von Neumann algebras and taking values in the algebra of bounded operators on a Hilbert space and particularly certain convex subsets of the set of such maps. We show that when one of the marginal maps of such a map is an extreme point, then the marginals uniquely determine the map. We will further prove that when both of the marginals are extreme, then the whole map is extreme. We show that this general result is the common source of several well-known results dealing with, e.g., jointly measurable observables. We also obtain new insight especially in the realm of quantum instruments and their marginal observables and channels.

scholarly journals Infinite dimensional generalizations of Choi’s Theorem

2019 ◽  
Vol 7 (1) ◽  
pp. 67-77
Author(s):  
Shmuel Friedland
Keyword(s):  
Hilbert Spaces ◽  
Quantum Channel ◽  
Trace Class ◽  
Natural Generalization ◽  
Linear Operators ◽  
Completely Positive Map ◽  
Completely Positive ◽  
Bounded Linear ◽  
Positive Map ◽  
Finite Dimensional

Abstract In this paper we give a simple sequence of necessary and sufficient finite dimensional conditions for a positive map between certain subspaces of bounded linear operators on separable Hilbert spaces to be completely positive. These criterions are natural generalization of Choi’s characterization for completely positive maps between pairs of linear operators on finite dimensional Hilbert spaces. We apply our conditions to a completely positive map between two trace class operators on separable Hilbert spaces. A completely positive map μ is called a quantum channel, if it is trace preserving, and μ is called a quantum subchannel if it decreases the trace of a positive operator.We give simple neccesary and sufficient condtions for μ to be a quantum subchannel.We show that μ is a quantum subchannel if and only if it hasHellwig-Kraus representation. The last result extends the classical results of Kraus and the recent result of Holevo for characterization of a quantum channel.

Complete Positivity of Two Class of Maps Involving Depolarizing and Transpose-Depolarizing Channels

2021 ◽  
Vol 28 (02) ◽  
Author(s):  
Xiuhong Sun ◽  
Yuan Li
Keyword(s):  
Sufficient Conditions ◽  
Linear Operators ◽  
Complete Positivity ◽  
Completely Positive Map ◽  
Completely Positive ◽  
Bounded Linear ◽  
Positive Map ◽  
Finite Dimensional ◽  
Necessary And Sufficient ◽  
Finite Dimensional Hilbert Space

In this note, we mainly study the necessary and sufficient conditions for the complete positivity of generalizations of depolarizing and transpose-depolarizing channels. Specifically, we define [Formula: see text] and [Formula: see text], where [Formula: see text] (the set of all bounded linear operators on the finite-dimensional Hilbert space [Formula: see text] is given and [Formula: see text] is the transpose of [Formula: see text] in a fixed orthonormal basis of [Formula: see text] First, we show that [Formula: see text] is completely positive if and only if [Formula: see text] is a positive map, which is equivalent to [Formula: see text] Moreover, [Formula: see text] is a completely positive map if and only if [Formula: see text] and [Formula: see text] At last, we also get that [Formula: see text] is a completely positive map if and only if [Formula: see text] with [Formula: see text] for all [Formula: see text] where [Formula: see text] are eigenvalues of [Formula: see text].

scholarly journals ASYMPTOTIC STABILITY I: COMPLETELY POSITIVE MAPS

2004 ◽  
Vol 15 (03) ◽  
pp. 289-312 ◽  
Author(s):  
WILLIAM ARVESON
Keyword(s):  
Asymptotic Behavior ◽  
Asymptotic Stability ◽  
Von Neumann Algebras ◽  
Completely Positive Map ◽  
Completely Positive Maps ◽  
Completely Positive ◽  
Locally Finite ◽  
Von Neumann ◽  
C Algebra ◽  
Positive Maps

We show that for every "locally finite" unit-preserving completely positive map P acting on a C*, there is a corresponding *-automorphism α of another unital C*-algebra such that the two sequences P, P2, P3, … and α, α2, α3, … have the same asymptotic behavior. The automorphism α is uniquely determined by P up to conjugacy. Similar results hold for normal completely positive maps on von Neumann algebras, as well as for one-parameter semigroups. These results are operator algebraic counterparts of the classical theory of Perron and Frobenius on the structure of square matrices with nonnegative entries.

scholarly journals Topological entropy for the canonical completely positive maps on graph C*-Algebras

2004 ◽  
Vol 70 (1) ◽  
pp. 101-116 ◽  
Author(s):  
Ja A. Jeong ◽  
Gi Hyun Park
Keyword(s):  
Topological Entropy ◽  
Finite Graph ◽  
Infinite Graph ◽  
Completely Positive Map ◽  
Completely Positive Maps ◽  
Completely Positive ◽  
Locally Finite ◽  
Finite Graphs ◽  
C Algebras ◽  
Positive Maps

Let C*(E) = C*(se, pv) be the graph C*-algebra of a directed graph E = (E0, E1) with the vertices E0 and the edges E1. We prove that if E is a finite graph (possibly with sinks) and φE: C*(E) → C*(E) is the canonical completely positive map defined by then Voiculescu's topological entropy ht(φE) of φE is log r(AE), where r(AE) is the spectral radius of the edge matrix AE of E. This extends the same result known for finite graphs with no sinks. We also consider the map φE when E is a locally finite irreducible infinite graph and prove that , where the supremum is taken over the set of all finite subgraphs of E.

On Approximately Finite-Dimensional Von Neuman Algebras, II

1978 ◽  
Vol 21 (4) ◽  
pp. 415-418 ◽  
Author(s):  
George A. Elliott
Keyword(s):  
Von Neumann Algebra ◽  
Von Neumann Algebras ◽  
Completely Positive Maps ◽  
Completely Positive ◽  
Von Neumann ◽  
Intrinsic Characterization ◽  
C Algebras ◽  
Finite Dimensional ◽  
Positive Maps ◽  
Injective Von Neumann Algebra

AbstractAn intrinsic characterization is given of those von Neumann algebras which are injective objects in the category of C*-algebras with completely positive maps. For countably generated von Neumann algebras several such characterizations have been given, so it is in fact enough to observe that an injective von Neumann algebra is generated by an upward directed collection of injective countably generated sub von Neumann algebras. The present work also shows that three of the intrinsic characterizations known in the countably generated case hold in general.

scholarly journals Asymmetric invariant sets for completely positive maps on C*-algebras

1986 ◽  
Vol 33 (3) ◽  
pp. 471-473 ◽  
Author(s):  
A. Guyan Robertson
Keyword(s):  
Invariant Sets ◽  
Completely Positive Map ◽  
Completely Positive Maps ◽  
Completely Positive ◽  
Positive Map ◽  
C Algebras ◽  
Positive Maps

Let A be a noncommutative C*-algebra other than M2(I). We show that there exists a completely positive map φ of norm one on A and an element a ɛ A such that φ(a) = a, φ(a*a) = a*a, but φ(aa*) ≠ aa*.

Dilations and Hahn Decompositions for Linear Maps

1981 ◽  
Vol 33 (4) ◽  
pp. 826-839 ◽  
Author(s):  
D. W. Hadwin
Keyword(s):  
Linear Operators ◽  
Completely Positive Maps ◽  
Linear Combinations ◽  
Completely Positive ◽  
Bounded Linear ◽  
Positive Maps ◽  
Linear Maps ◽  
Positive Linear Map ◽  
Finite Linear ◽  
Analogous Class

Suppose is a C*-algebra and H is a Hilbert space. Let denote the set of completely positive maps from into the set B(H) of (bounded linear) operators on H. This paper studies the vector space spanned by , i.e., the linear maps that are finite linear combinations of completely positive maps. From another viewpoint, a map ϕ is in precisely when it has a decomposition ϕ = (ϕ1 – ϕ2) + i(ϕ3 – ϕ4) with ϕ1, ϕ2, ϕ3, ϕ4 in CP ; this decomposition is analogous to the Hahn decomposition for measures [8, 111.4.10] (see also Theorem 20). The analogous class of maps with “completely positive” replaced by “positive” was studied by R. I. Loebl [11] and S.-K. Tsui [17], and when is commutative, this latter class coincides withi , since every positive linear map on a commutative C*-algebra is completely positive [16].

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