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arXiv 0911.0179math.DSmath-phmath.MPquant-ph
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量子信息中密度矩阵的热力学形式

A Thermodynamic Formalism for density matrices in Quantum Information

A. Baraviera, C. F. Lardizabal, Artur O. Lopes, M. Terra Cunha

摘要:

本文考虑了作用于密度矩阵的定态系统的熵和压力的新概念,推广了遍历理论中常用的概念。我们的工作的一部分是证明为什么我们在这里描述的定义和结果是热力学形式主义(在R。Bowen,Y. Sinai和D. Ruelle)。众所周知,在我们考虑量子形式主义的情况下,密度算符的概念应该取代测度的概念。考虑作用在有限$N$维复Hilbert空间$$ Λ(ρ):=\sum_{i=1}^k tr(W_iρW_i^*)\frac{V_iρV_i^*}{tr(V_iρV_i^*)}, $$上的密度矩阵空间$\mathcal{M}_N$上的算子$Λ$,其中$W_i$和$V_i$,$i=1,2,..., k$是该Hilbert空间中的线性算子.在某种意义上,这个运算符是迭代函数系统(IFS)的一个版本。即,$V_i\,(.)\,V_i^*=:F_i(.)$、$i=1,2,...,k$起反向分支的作用(即,密度矩阵的配置空间上的动力学),并且$W_i$扮演可以在IFS上考虑的权重的角色。以这种方式,族$W:=\{W_i\}_{i=1,..., k}$确定量子迭代函数系统(QIFS)。我们还提出了一些估计相关的Holevo界。

英文摘要:

We consider new concepts of entropy and pressure for stationary systems acting on density matrices which generalize the usual ones in Ergodic Theory. Part of our work is to justify why the definitions and results we describe here are natural generalizations of the classical concepts of Thermodynamic Formalism (in the sense of R. Bowen, Y. Sinai and D. Ruelle). It is well-known that the concept of density operator should replace the concept of measure for the cases in which we consider a quantum formalism. We consider the operator $Λ$ acting on the space of density matrices $\mathcal{M}_N$ over a finite $N$-dimensional complex Hilbert space $$ Λ(ρ):=\sum_{i=1}^k tr(W_iρW_i^*)\frac{V_iρV_i^*}{tr(V_iρV_i^*)}, $$ where $W_i$ and $V_i$, $i=1,2,..., k$ are linear operators in this Hilbert space. In some sense this operator is a version of an Iterated Function System (IFS). Namely, the $V_i\,(.)\,V_i^*=:F_i(.)$, $i=1,2,...,k$, play the role of the inverse branches (i.e., the dynamics on the configuration space of density matrices) and the $W_i$ play the role of the weights one can consider on the IFS. In this way a family $W:=\{W_i\}_{i=1,..., k}$ determines a Quantum Iterated Function System (QIFS). We also present some estimates related to the Holevo bound.

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