Quantum mechanics describes microscopic physics, while physics at large scale is governed by general relativity. The unification of these two theories, called quantum gravity, is expected to reveal the origin of our universe and is obviously an ultimate goal of theoretical physics. Superstring theory is known as the most promising candidate to achieve this goal. Therefore I am exploring new predictions of quantum gravity arising from superstring theory.　

Specifically, we constructed the first exactly solvable and dynamical model of quantum gravity that is completely stable. Even though its spacetime is two-dimensional and looks like a toy model, at present this is virtually the only string theory where we can compute everything exactly. In this model, called a type 0 matrix model, we can deal with multiple universes at the same time and consider quantum mechanical mixing between them.

I am currently interested in applying to quantum gravity the idea of entanglement entropy, which is an important component of quantum information theory. This offers us a new microscopic understanding of the Bekenstein-Hawking entropy of black holes. We have also developed a differential geometry interpretation of quantum information theory.