KITANO, Masao

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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.