KITANO, Masao

本研究的目的是光子对在高灵敏度光学测量中的应用。参量下转换产生的光子对表现出经典理论无法理解的奇异行为。特别是利用光子对的同时性可以产生光子数本征态。本项目总结如下：1。光子对的量子相关理论通常是用量子场论来研究光子对的。然而，在这种方法中，不容易获得光子相关和高阶干涉的直观图像。作为一种替代方法，我们引入了服从薛定谔方程的双光子波函数。在这种观点下，光子对表现为二维构型空间中的波。根据Leinass-Myrheim方法，玻色子波必须是对称的。利用双光子波函数，我们可以对各种双光子相关现象有一个统一的认识。结果表明，玻色子对称性和参量荧光的光谱特性对量子相关有贡献。我们也看到了光子对和双电子系统之间的一些相似之处，例如氦原子和有机染料。我们首先计划了参量下转换产生的光子对的实验。然而，在研究过程中，我们提出了一种新的光子数的量子不破坏测量方案。因此，我们转向实验来验证我们的方案。该原理是基于被测光引起的虚跃迁引起的原子能级位移。在初步实验中，我们可以在不吸收的情况下测量光强。虽然目前达到的灵敏度太低，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测量中。

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.