The University of Tokyo · Physics and Astronomy
Professor Yoshiko Ogata's research lab specializes in mathematical physics and quantum many-body systems, with a focus on quantum spin chains and two-dimensional quantum spin systems. The lab investigates nonequilibrium dynamics, quantum phase transitions, and topological phases, particularly symmetry-protected topological order in quantum systems. Key interests include the algebraic structures underlying gapped ground states, such as braided C*-tensor categories, and the application of operator algebra methods to statistical mechanics and large deviation theory.
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We investigate the nonequilibrium properties of the transverse XX chain. The steady state can be interpreted as the equilibrium state or the ground state of the effective Hamiltonian, which depends on the initial state. We also study the physical properties of the state at various temperatures, in particular, the effects of quantum phase transition.
We investigate the magnetization profile in the intermediate time of diffusion by using the C*-algebraic method. We observe a transition from monotone profile to nonmonotone profile. This transition is purely thermal.
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We derive braided C*-tensor categories from gapped ground states on two-dimensional quantum spin systems satisfying some additional condition, which we call the approximate Haag duality.
Abstract We consider symmetry-protected topological phases with on-site finite group G symmetry $\beta $ for two-dimensional quantum spin systems. We show that they have $H^{3}(G,{\mathbb T})$ -valued invariant.
We recover, expand, and unify quantum (and classical) large deviation results for lattice Gibbs states. The main new ingredient in this paper is a control on the overlap of spectral projections for non-commutative observables. Our proof of large deviations is based on Ruelle–Lanford functions [20, 34] which establishes the existence of a rate function directly by subadditivity arguments, as done in the classical case in [23, 32], instead of relying on Gärtner–Ellis theorem, and cluster expansion
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