The Hakubi Project

Under the recent COVID-19 pandemic, we are recommended or needed to measure the temperature of ourselves every day. The temperatures of matters (materials, animals, vegetables, etc.) can be defined and measured in most cases. But, how about light? Can we define and measure the temperature of light? The answer is ... yes, we can but only in limited situations. The temperature can be defined in thermal equilibrium situations. The light exists mostly in non-equilibrium situations. Thus, the concept of temperature usually does not appear in the physics of light. But, in this seminar, I will talk about the physics of light at low temperature along a physical phenomenon called the superradiant phase transition, which I am studying in recent years.