Rank-preserving module maps

Nonlinear maps preserving Jordan $η$-$\ast$-$n$-products

Let $η\neq -1$ be a non-zero complex number, and let $ϕ$ be a not necessarily linear bijection between two von Neumann algebras, one of which has no central abelian projections preserving the Jordan $η$-$\ast$-$n$-product. It is showed that $ϕ$ is a linear $\ast$-isomorphism if $η$ is not real and $ϕ$ is the sum of a linear $\ast$-isomorphism and a conjugate linear $\ast$-isomorphism if $η$ is real.

Additive mappings in algebras of unbounded operators preserving operators of rank one

Let $ \mathcal D$ be a dense linear manifold in a Hilbert space $\mathcal H$ and let $L^+(\mathcal D)$ be the *-algebra of all linear operators $A$ such that $A \mathcal D \subset \mathcal D, A^* \mathcal D \subset \mathcal D$. Denote by $F(\mathcal D)$ the *-ideal of $L^+(\mathcal D)$ consisting of all finite-rank operators. A characterization of the structure of additive mappings of $F(\mathcal D)$ preserving operators of rank one or projections of rank one is given. The corresponding results for algebras of bounded operators on Banach spaces were given by P. uSemrl.

II$_1$-型因子上的秩度量等距与保行列式映射

Rank metric isometries and determinant-preserving mappings on II$_1$-factors

该研究完整刻画了II$_1$-型因子对应的Murray--von Neumann代数上秩度量等距的一般形式，借此在II$_1$-型因子场景下证明Frobenius定理，证实了1996年的Harris--Kadison猜想。

Linear maps between C*-algebras preserving extreme points and strongly linear preservers

We study new classes of linear preservers between C$^*$-algebras and JB$^*$-triples. Let $E$ and $F$ be JB$^*$-triples with $\partial_{e} (E_1)$. We prove that every linear map $T:E\to F$ strongly preserving Brown-Pedersen quasi-invertible elements is a triple homomorphism. Among the consequences, we establish that, given two unital C$^*$-algebras $A$ and $B,$ for each linear map $T$ strongly preserving Brown-Pedersen quasi-invertible elements, then there exists a Jordan $^*$-homomorphism $S: A\to B$ satisfying $T(x) = T(1) S(x)$, for every $x\in A$. We also study the connections between linea…

Schur null preserving maps

We provide a characterisation of Schur multiplicative maps on both finite and infinite dimensional matrix spaces, and show that every surjective Schur multiplicative contraction is automatically an isometry. We also generalise this result and provide a characterisation of Schur null preserving maps on $m\times n$ matrices and on Schur multipliers.

$C^*$-代数上的乘法谱保持映射

Multiplicatively spectrum-preserving maps on $C^{*}$-algebras

本文刻画含单位元$C^*$-代数自伴元之间的乘法谱保持满射，证明其由Jordan同构与中心对称决定，并解答Molnár的问题。

Linear maps preserving separability of pure states

Linear maps preserving pure states of a quantum system of any dimension are characterized. This is then used to establish a structure theorem for linear maps that preserve separable pure states in multipartite systems. As an application, a characterization of separable pure state preserving affine maps is obtained.

Maps completely preserving involution

Let X and Y be Banach spaces with dim X greater than 3. Let A and B be standard operator algebras on X and Y. We characterize the form of maps from A onto B such that completely preserve involution.

Maps completely preserving the quadratic operators

Let $\mathcal{A}$ and $\mathcal{B}$ be standard operator algebras on Banach spaces $\mathcal{X}$ and $\mathcal{Y}$, respectively. In this paper, we show that every bijection completely preserving quadratic operators from $\mathcal{A}$ onto $\mathcal{B}$ is either an isomorphism or (in the complex case) a conjugate isomorphism.

Maps preserving the spectrum of certain products of operators

Let H be a complex Hilbert space, B(H) and S(H) be the spaces of all bounded operators and all self-adjoint operators on H, respectively. We give the concrete forms of the maps on B(H) and also S(H) which preserve the spectrum of certain products of operators.

Positive maps which are bijective on the set of rank projections

Extending Wigner's theorem we give a characterization of positive maps of $B(H)$ into itself which map the set of rank k projections onto itself.

Nonlinear maps preserving sums of triple products on $\ast $-algebras

Let $\mathcal{A}$ and $\mathcal{B}$ be two unital complex $\ast $-algebras such that $\mathcal{A}$ has a nontrivial projection. In this paper, we study the structure of bijective nonlinear maps $Φ:\mathcal{A}\rightarrow \mathcal{B}$ preserving sum of triple products $α_{1} abc+α_{2} a^{*}cb^{*}+α_{3} ba^{*}c +α_{4} cab^{*}+α_{5} bca+α_{6} cb^{*}a^{*},$ where the scalars $\{α_{k}\}_{k=1}^{6}$ are complex numbers satisfying some conditions.

Maps preserving the Douglas solution of operator equations

We consider bijective maps $ϕ$ on the full operator algebra $\mathcal{B}(\mathcal{H})$ of an infinite dimensional Hilbert space with the property that, for every $A,B,X\in \mathcal{B}(\mathcal{H})$, $X$ is the Douglas solution of the equation $A=BX$ if and only if $Y=ϕ(X)$ is the Douglas solution of the equation $ϕ(A)=ϕ(B)Y$. We prove that those maps are implemented by a unitary or anti-unitary map $U$, i.e., $ϕ(A)=UAU^*$.

Strong skew commutativity preserving maps on von Neumann algebras

Let ${\mathcal M}$ be a von Neumann algebra without central summands of type $I_1$. Assume that $Φ:{\mathcal M}\rightarrow {\mathcal M}$ is a surjective map. It is shown that $Φ$ is strong skew commutativity preserving (that is, satisfies $Φ(A)Φ(B)-Φ(B)Φ(A)^*=AB-BA^*$ for all $A,B\in{\mathcal M}$) if and only if there exists some self-adjoint element $Z$ in the center of ${\mathcal M}$ with $Z^2=I$ such that $Φ(A)=ZA$ for all $A\in{\mathcal M}$. The strong skew commutativity preserving maps on prime involution rings and prime involution algebras are also characterized.

Linear maps on the space of all bounded observables preserving maximal deviation

In this paper we determine all the bijective linear maps on the space of bounded observables which preserve a fixed moment or the variance. Nonlinear versions of the corresponding results are also presented.

2-positive almost order zero maps and decomposition rank

We consider 2-positive almost order zero (disjointness preserving) maps on C*-algebras. Generalizing the argument of M. Choi for multiplicative domains, we give an internal characterization of almost order zero for 2-positive maps. It is also shown that complete positivity can be reduced to 2-positivity in the definition of decomposition rank for unital separable C*-algebras.

Additive maps preserving idempotency of products or Jordan products of operators

Let H and K be infinite dimensional Hilbert spaces, while B(H) and B(K) denote the algebras of all linear bounded operators on H and K, respectively. We characterize the forms of additive mappings from B(H) into B(K) that preserve the nonzero idempotency of either Jordan products of operators or usual products of operators in both directions.

A Characterization of Completely-Positive Trace-Preserving Maps on 2x2 Matrices

This paper has been superseded by quant-ph/0101003.

Maps on positive cones in operator algebras preserving power means

In this paper we consider power means of positive Hilbert space operators both in the conventional and in the Kubo-Ando senses. We describe the corresponding isomorphisms (bijective transformations respecting those means as binary operations) on positive definite cones and on positive semidefinite cones in operator algebras. We also investigate the question when those two sorts of power means can be transformed into each other.

Hilbert isometries and maximal deviation preserving maps on JB-algebras

In this paper we characterize the surjective linear variation norm isometries on JB-algebras. Variation norm isometries are precisely the maps that preserve the maximal deviation, the quantum analogue of the standard deviation, which plays an important role in quantum statistics. Consequently, we characterize the Hilbert's metric isometries on cones in JB-algebras.

Fidelity preserving maps on density operators

We prove that any bijective fidelity preserving transformation on the set of all density operators on a Hilbert space is implemented by an either unitary or antiunitary operator on the underlying Hilbert space.

Maps preserving trace of products of matrices

We prove the linearity and injectivity of two maps $ϕ_1$ and $ϕ_2$ on certain subsets of $M_n$ that satisfy $\operatorname{tr}(ϕ_1(A)ϕ_2(B))=\operatorname{tr}(AB)$. We apply it to characterize maps $ϕ_i:\mathcal{S}\to \mathcal{S}$ ($i=1, \ldots, m$) satisfying $$\operatorname{tr} (ϕ_1(A_1)\cdots ϕ_m(A_m))=\operatorname{tr} (A_1\cdots A_m)$$ in which $\mathcal{S}$ is the set of $n$-by-$n$ general, Hermitian, or symmetric matrices for $m\ge 3$, or positive definite or diagonal matrices for $m\ge 2$. The real versions are also given.