Origin of the Universe
A significant objective of my research is to understand the origin of the universe and the processes that have shaped its development to the present day. In addressing the formation of the universe, several cosmological issues such as the flatness problem and the horizon problem emerge from current observational data. The theory of cosmic inflation has been proposed as a means of resolving these issues in a manner consistent with the observable universe. Cosmic inflation refers to the rapid, exponential expansion of the universe that is believed to have occurred between 10-36 and 10-34 seconds after the inception of the universe. Therefore, the validation of inflationary theory and the precise observation of the inflationary epoch are critical to gaining a comprehensive understanding of the universe’s origin and its subsequent evolution.
Gravitational Waves
Gravitational waves is a phenomenon predicted by Einstein’s general relativity, where distortions in spacetime propagates as waves. The detection of gravitational waves from a binary black hole merger by the Advanced LIGO in 2015 marked the inception of gravitational astronomy, offering a new means of observing the universe. A significant advantage of gravitational waves is that they can be observed even in the absence of electromagnetic radiation, as they interact very weakly with matter and are generally not obstructed by it. For example, during the early stages of the universe, up to approximately 380,000 years after its birth, photons could not travel freely due to interactions with electrons. Although secondary effects of cosmic inflation can be captured through electromagnetic waves, capturing the entirety of information about cosmic inflation has remained elusive. In other words, the observation of gravitational waves from the early universe holds the potential to decisively confirm the inflationary theory.
Interferometer
An interferometer is a precision instrument that measures minute changes in distance by utilizing the interference of light. It functions by splitting a laser beam into two separate paths, reflecting them back, and then recombining them to form an interference pattern. Variations in the relative lengths of the two paths lead to shifts in the interference pattern, enabling the detection of extremely small displacements. When a gravitational wave arrives, it causes slight distortions in spacetime, which in turn induce tiny changes in the lengths of the interferometer’s arms.
Thus, in order to observe gravitational waves, it is necessary to precisely detect these minute changes. However, the typical strain induced by gravitational waves is extremely small, on the order of 10-24, and the sensitivity is limited by various factors. My primary research focuses on developing methods to reduce quantum noise, which originates from the quantum nature of laser light and predominantly limits the sensitivity, as well as mitigating thermal effects caused by the absorption of laser light in the optical components of the interferometer.