In recent years, the realization of quantum technology has attracted a great deal of attention as a technology that brings innovation to various fields such as measurement, information processing, and processing. One of the important things to realize quantum technology is to identify the factors that destroy the coherence of the quantum system (decoherence) and protect the quantum system from the decoherence.
 Introducing research on spin coherence of cryogenic rubidium atomic gas as the first topic of this lecture. Introducing new coherence control methods and quantum phenomena such as coherence control by spin echo method and application to magnetic field measurement technology {1} and coherence formation by particle dissipation {2}, focusing on the research that the lecturer has done so far. .. As the second topic, we will introduce how to control and utilize the quantum fluctuations of light, especially its application to nonlinear optical microscopes. A non-linear optical microscope is a method that enables deep observation of a living body by utilizing the non-linear interaction between light and a substance.
 The speaker recently succeeded in experimentally demonstrating that the observation performance in the depth direction of a nonlinear optical microscope can be improved by using the ultrafast intensity correlation of several hundred femtoseconds created by the quantum fluctuation of the pulse pair {3. }. Although this method utilizes quantum fluctuations, it has an important application feature of being resistant to loss.
 In the lecture, we also discussed the further possibility of photon fluctuation in nonlinear measurement.