Our group investigates fundamental problems in condensed matter physics, such as critical phenomena in quantum magnets and superfluid, based on massively parallel computation on ISSP supercomputers and "K-computer" at Kobe. For example, we are trying to find a "deconfined" critical phenimena, a new category of quantum phase transition, as a transition between Neel state and VBS state in the SU(N) Heisenberg model. Our recent computational results are in favor of the continuous transition predicted by the 1/N expansion theory, and we are planning a larger computation on K-computer for more conclusive results. In addition, the list of our research subjects includes novel quantum states and supersolids in ultra-cold atoms trapped in optical lattices, the incommensurate super-solid phase in particular, computation of entanglement spectrum of a VBS state, and developement of new methods for quantum frustrated systems based on tensor networks.
The "conventional" picture of the super solid. The deviation from a commensurate filling is responsible for the super current.
Phase diagram of the Bose-Hubbard model on the cubic lattice with the hopping constant t and the on-site repulsion U. There are the checker-board phase (CB), the superfluid phase (SF), the Mott insurator phase (MI), and the super solid phase (SS). The super-solid phase exists even at the commensurate filling.
Search for novel quantum phases and quantum transitions
Numerical methods for many-body physics, such as quantum Monte Carlo techniques and tensor network methods