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arXiv 1207.0992quant-ph
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能量本征态的精确相空间定域投影

Exact Phase Space Localized Projectors from Energy Eigenstates

J. J. Halliwell

摘要:

在从量子理论研究经典性的出现时,一个有用的步骤是构造对应于系统驻留在相空间区域的经典概念的量子算符。最简单的这种构造,使用相干态,产生近似投影算子的算子-它们的本征值近似等于1或0。这样的预测可能会被证明有接近经典的行为下的时间演化和这些结果已被用来证明一些有用的结果涌现经典的退相干历史方法的量子理论。在这里,我们将展示如何使用本征态的一个适当选择的哈密顿量来构建精确的投影算子是本地化的相位区域。我们阐明这些运营商的性质,并探讨其时间演化。对于谐振子的特殊情况下,时间演化是特别简单的,我们发现套相空间本地化的历史,这是完全退相干的任何初始状态和经典演化的概率为1。这些结果表明,如何近似退相干的历史和经典的预测相空间的历史可能是准确的,在某些情况下。

英文摘要:

In investigations of the emergence of classicality from quantum theory, a useful step is the construction of quantum operators corresponding to the classical notion that the system resides in a region of phase space. The simplest such constructions, using coherent states, yield operators which are approximate projection operators -- their eigenvalues are approximately equal to 1 or 0. Such projections may be shown to have close to classical behaviour under time evolution and these results have been used to prove some useful results about emergent classicality in the decoherent histories approach to quantum theory. Here, we show how to use the eigenstates of a suitably chosen Hamiltonian to construct exact projection operators which are localized on regions of phase. We elucidate the properties of such operators and explore their time evolution. For the special case of the harmonic oscillator, the time evolution is particularly simple, and we find sets of phase space localized histories which are exactly decoherent for any initial state and have probability 1 for classical evolution. These results show how approximate decoherence of histories and classical predictability for phase space histories may be made exact in certain cases.

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