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arXiv quant-ph/0212062quant-ph
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量子态的锥表示与非保迹量子运算

The Conal representation of Quantum States and Non Trace-Preserving Quantum Operations

Pablo Arrighi, Christophe Patricot

摘要:

我们表示广义密度矩阵的$d$ -复杂的维量子系统作为一个子锥的一个真正的点锥的旋转在$\mathbb{R}^{d^2}$,或实际上是一个闵可夫斯基锥在$\mathbb{E}^{1,d^2-1}$。广义纯态对应于$\mathbb{E}^{1,d^2-1}$的某些未来指向的类光矢量。广义布洛赫球的这种扩展使我们能够满足非保迹量子操作,特别是查看广义测量的每结果效应。我们表明,这些包括产品的正交变换的轴的旋转锥和一个积极的真正的线性变换。我们给出了单量子比特情况下的详细公式,并用初始状态向量和测量向量来表示测量后状态。我们应用这些结果,以找到两个等概率纯态的情况下的信息增益与干扰权衡。因此,我们恢复Fuchs和Peres的公式在一个优雅的方式。

英文摘要:

We represent generalized density matrices of a $d$-complex dimensional quantum system as a subcone of a real pointed cone of revolution in $\mathbb{R}^{d^2}$, or indeed a Minkowskian cone in $\mathbb{E}^{1,d^2-1}$. Generalized pure states correspond to certain future-directed light-like vectors of $\mathbb{E}^{1,d^2-1}$. This extension of the Generalized Bloch Sphere enables us to cater for non-trace-preserving quantum operations, and in particluar to view the per-outcome effects of generalized measurements. We show that these consist of the product of an orthogonal transform about the axis of the cone of revolution and a positive real linear transform. We give detailed formulae for the one qubit case and express the post-measurement states in terms of the initial state vectors and measurement vectors. We apply these results in order to find the information gain versus disturbance tradeoff in the case of two equiprobable pure states. Thus we recover Fuchs and Peres' formula in an elegant manner.

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