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arXiv quant-ph/0412030quant-ph
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量子系统中的广义测不准关系和有效测量

Generalized uncertainty relations and efficient measurements in quantum systems

V. P. Belavkin

摘要:

我们考虑两个变种的量子统计推广的Cramer-Rao不等式,建立了一个不变的下限上的均方误差的广义量子测量。这个不等式的复杂变形导致了任意状态的广义不确定原理的精确表述,与Helstrom的对称变形相反,在Helstrom的对称变形中,这些关系只针对纯态获得。引入了正则态的概念,并给出了正则态参数,特别是李群正则参数估计的均方误差下界。结果表明,这些边界是全球可达到的,只有对规范的状态,存在有效的测量或quasimeasurements。

英文摘要:

We consider two variants of a quantum-statistical generalization of the Cramer-Rao inequality that establishes an invariant lower bound on the mean square error of a generalized quantum measurement. The proposed complex variant of this inequality leads to a precise formulation of a generalized uncertainty principle for arbitrary states, in contrast to Helstrom's symmetric variant in which these relations are obtained only for pure states. A notion of canonical states is introduced and the lower mean square error bound is found for estimating of the parameters of canonical states, in particular, the canonical parameters of a Lie group. It is shown that these bounds are globally attainable only for canonical states for which there exist efficient measurements or quasimeasurements.

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