KITANO, Masao

本研究项目的目的是将光子对应用于高灵敏度的光学测量。通过参数下转换产生的光子对显示出用经典理论无法理解的奇怪行为。特别是每一对的同时性可以用来产生光子数本征态。本课题的主要内容如下：1.光子对的量子关联理论传统上，量子场论被用于光子对的研究。然而，在这种方法中，要获得光子关联和高阶干涉的直观图像并不容易。作为另一种方法，我们引入了服从薛定谔方程的双光子波函数。在这个观点中，光子对在二维构型空间中表现为波。根据Leinass-Myheim方法，玻色波必须对称。利用双光子波函数，我们可以得到对各种双光子关联现象的统一看法。结果表明，玻色子的对称性和参量荧光的光谱性质对量子关联有贡献。我们也看到了光子对和两电子系统之间的一些相似之处，例如氦原子和有机染料。光移法量子非破坏测量光子数我们首先计划对由参数下转换产生的光子对进行实验。然而，在研究过程中，我们得到了一种新的量子非破坏测量光子数的方案。因此，为了验证我们的方案，我们切换到了实验。其原理是基于被测量光引起的虚跃迁引起的原子能级移动。在初步实验中，我们可以在没有吸收的情况下测量光强。虽然到目前为止达到的灵敏度太低，无法检测到量子噪声，但我们希望我们的方案能够扩展到真正的QND测量。

The purpose of this research project is applications of photon pairs to high-sensitive optical measurements. The photon pair generated through parametric down-conversion shows strange behaviors that cannot be understood in terms of classical theories. Especially the simultaneity of each pair can be utilized for generation of photon-number eigenstates. The summary of this project is as follows :1. Theory for quantum-correlation of photon pairs Conventionally the quantum field theory is used in the study of photon pairs. In that approach, however, it is not easy to obtain intuitive pictures for photon correlations and the higher-order interference. As an alternative approach, we have introduced the two-photon wavefunction which obeys Schrodinger's equation. In this view, the photon pair behaves as a wave in a two dimensional configuration space. The bosonic wave has to be symmetrized according to the Leinass-Myrheim method. Using the two-photon wave function, we could obtain a unified view for various two-photon correlation phenomena. It turned out that the bosonic symmetry and the spectral property of parametric fluorescence contribute to the quantum correlation. We have also seen some analogies between photon pairs and two-electron systems such as helium atoms and organic dyes.2. Quantum non-demolition measurement of photon number with light shift We first planned experiments on photon pairs generated by parametric down-conversions. In the course of research, however, we came to a new scheme of quantum non-demolition measurement of photon number. Thus we switched to the experiments in order to verify our scheme. The principle is based on the atomic level shifts due to the virtual transition induced by the light to be measured. In the preliminary experiment we could measure the light intensity without the absorption. Although the sensitivity so far reached is too low to detect the quantum noise, we hope our scheme will be extended to a real QND measurement.