Theory of quantum many-body systems

We theoretically study physics of quantum many-body (QMB) systems, in which constituents obey the laws of the quantum mechanics. Examples include electrons in solids, liquid helium, ultracold gases, and quantum computers. In QMB systems, many counter-intuitive phenomena emerge thanks to the cooperation/competition of quantum effects and interparticle interactions. Specifically, we are interested in superfluidity, superconductivity, supersolidity, Kondo effects, quantum magnetism, quantum phase transitions, non-equilibrium dynamics, many-body localization, etc.

One of the severest difficulties in theoretical analyses of QMB systems lies in the fact that the numerical cost for describing a QMB system grows in general exponentially with the size of the system. Hence, in order to perform numerical analyses of realistic experiments of a QMB system, one needs efficient theoretical/numerical methods that circumvent such exponential growth of the numerical cost. We utilize and develop several numerical methods for QMB systems, such as matrix product states, cluster mean-field theory, and truncated Wigner approximation.

In recent years, analog quantum simulation has attracted much attention as a new tool for studying QMB physics. A quantum simulator mimics complex phenomena emerging in a real material by using an artificial QMB system with high controllability, including ultracold gases and trapped ions. We strongly support development/invention of quantum simulators in some experimental groups from a theoretical standpoint.

Ongoing projects

Research titleProgram titleSponsorTermAmount (K JPY)Role
Novel quantum many-body phenomena pioneered by means of tensor-network methods and quantum simulatorsFORESTJSTApr. 2021 – Mar. 202320,000PI
Experimental study of open quantum many-body systems using strongly-correlated cold atomic gasesKAKENHI
JSPSApr. 2021 – Mar. 20231,400Collaborator
Development of cold-atom quantum simulators on the basis of spatio-temporal optical control at the attosecond-nanometer level and its application to quantum computations Q-LEAP Flagship program
Fundamental research
MEXTNov. 2019 ~ Mar. 202925,400Collaborator
Developing innovative optical-lattice quantum simulators on the basis of high controllability of ultracold gases CRESTJSTOct. 2016 ~ Mar. 202226,200Collaborator
Pioneering novel quantum many-body physics with orbital and spin degrees of freedom of ultracold gases in optical lattices KAKENHI
JSPSJul. 2018 ~ Mar. 202315,000Collaborator

Projects in the past

Realizing quantum gravity with both holographic principle and ultracold gases in optical latticesKAKENHI
JSPSApr. 2018 ~ Mar. 20213,300PI
Novel quantum phases pioneered by ultimate control and observation of Ytterbium quantum gases KAKENHI
JSPSJul. 2013 ~ Mar. 20184,000Collaborator
Quantum phase transitions and non-equilibrium dynamics of one-dimensional quantum fluid in non-uniform potentials KAKENHI KIBAN(C)JSPSApr. 2013~Mar. 20162,900PI
Dynamics of strongly correlated Bose gases in optical lattices RIKEN SPR’s FundingRIKENApr. 2010 ~ Sep. 20123,000PI
Realizing quantum Fermi-Pasta-Ulam recurrence with ultracold gases KAKENHI
JSPSAug. 2010~ Mar. 20111,250PI
Breakdown of superflow in Bose gases in optical lattices KAKENHI
JSPS fellow’s funding
JSPSApr. 2008 ~ Mar. 20101,600PI
Spontaneous symmetry breaking and elementary excitations in Bose-Einstein condensed systems KAKENHI
JSPS fellow’s funding
JSPSApr. 2005 ~ Mar. 20082,700PI