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arXiv quant-ph/9907057quant-ph
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玻色子场的经典测量与量子测量的对应

On the correspondence between classical and quantum measurements on a bosonic field

G. M. D'Ariano, M. F. Sacchi, H. P. Yuen

摘要:

研究了描述单模玻色子场的谐振子的经典测量和量子测量之间的对应关系。我们将场的可观测量的量子测量与通过量子放大器理想地放大可观测量的可能性联系起来。"经典"测量对应于谐振子的位置$q$和动量$p$的联合测量,具有结果$α=q+ip$的函数$f$的以下评估。对于电磁场的联合测量是通过外差探测器实现的。通过$\hat O$的理想放大器对外差探测器进行预放大,并通过增益$g$对结果进行重新标度,从而获得可观测$\hat O$的量子测量。我们给出了一个一般的判据,说明在无限增益的极限下,这种前置放大外差探测方案何时接近$\hat O$的理想量子测量。我们表明,这一标准是满意的,实现了理想的测量的情况下的光子数算子和正交。对于这两个运营商的方法是强大的外差探测器的非单位量子效率。另一方面,我们表明,前置放大外差检测方案不适用于任意可观测的领域。作为一个反例,我们证明了简单的二次函数的字段$\hat K=i(a^{†2}-a^2)/2$没有相应的多项式函数$f(α,\bar α)$-包括明显的选择$f=\hbox{Im}(α^2)$-允许测量$\hat K$通过前置放大外差测量方案。

英文摘要:

We study the correspondence between classical and quantum measurements on a harmonic oscillator that describes a one-mode bosonic field. We connect the quantum measurement of an observable of the field with the possibility of amplifying the observable ideally through a quantum amplifier. The ``classical'' measurement corresponds to the joint measurement of the position $q$ and momentum $p$ of the harmonic oscillator, with following evaluation of a function $f$ of the outcome $α=q+ip$. For the electromagnetic field the joint measurement is achieved by a heterodyne detector. The quantum measurement of an observable $\hat O$ is obtained by preamplifying the heterodyne detector through an ideal amplifier of $\hat O$, and rescaling the outcome by the gain $g$. We give a general criterion which states when this preamplified heterodyne detection scheme approaches the ideal quantum measurement of $\hat O$ in the limit of infinite gain. We show that this criterion is satisfied and the ideal measurement is achieved for the case of the photon number operator and for the quadrature. For both operators the method is robust to nonunit quantum efficiency of the heterodyne detector. On the other hand, we show that the preamplified heterodyne detection scheme does not work for arbitrary observable of the field. As a counterexample, we prove that the simple quadratic function of the field $\hat K=i(a^{†2}-a^2)/2$ has no corresponding polynomial function $f(α,\bar α)$---including the obvious choice $f=\hbox{Im}(α^2)$---that allows the measurement of $\hat K$ through the preamplified heterodyne measurement scheme.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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