BlandNew of Masayuki Ohzeki Kyoto University

Duality analysis and its application: bond percolation
Masayuki Ohzeki

Phys. Rev. E 87, 012137 (2013)

DSC08697.JPGOn a moutain in Austria
We obtain the exact solution of the bond-percolation thresholds with inhomogenous probabilities on the square lattice. Our method is based on the duality analysis with real-space renormalization, which is a profound technique invented in the spin-glass theory. Our formulation is a more straightforward way compared to the very recent study on the same problem [R. M. Ziff, et. al., J. Phys. A: Math. Theor. 45 (2012) 494005]. The resultant generic formulas from our derivation can give several estimations for the bond-percolation thresholds on other lattices rather than the square lattice.


Duality analysis on random planar lattice
Masayuki Ohzeki, and Keisuke Fujii

LinkIconPhys. Rev. E 86, 051121 (2012)

DSC08794.JPGWu's message motivates me.The conventional duality analysis is employed to identify a location of a critical point on a uniform lattice without any disorder in its structure. In the present study, we deal with the random planar lattice, which consists of the randomized structure based on the square lattice. We introduce the uniformly random modification by the bond dilution and contraction on a part of the unit square. The random planar lattice includes the triangular and hexagonal lattices in extreme cases of a parameter to control the structure. The duality analysis in a modern fashion with real-space renormalization is found to be available for estimating the location of the critical points with wide range of the randomness parameter. As a simple testbed, we demonstrate that our method indeed gives several critical points for the cases of the Ising and Potts models, and the bond-percolation thresholds on the random planar lattice. Our method leads to not only such an extension of the duality analyses on the classical statistical mechanics but also a fascinating result associated with optimal error thresholds for a class of quantum error correction code, the surface code on the random planar lattice, which known as a skillful technique to protect the quantum state.


Fluctuation Theorems on Nishimori line
Masayuki Ohzeki

LinkIconPhys. Rev. E 86, 061110 (2012)

DSC08251.JPGAquarium in KyotoThe distribution of the performed work for spin glasses with gauge symmetry is considered. With the aid of the gauge symmetry, which leads to the exact/rigorous results in spin glasses, we find a fascinating relation of the performed work as the fluctuation theorem. The integral form of the resultant relation reproduces the Jarzynski-type equation for spin glasses we have obtained. We show that similar relations can be established not only for the distribution of the performed work but also that of the free energy of spin glasses with gauge symmetry, which provides another interpretation of the phase transition in spin glasses.


Measurement-Based Quantum Computation on Symmetry Breaking Thermal States
Keisuke Fujii, Yoshihumi Nakata, Masayuki Ohzeki and Mio Murao

submitted to Phys. Rev. Lett.

CIMG1171.JPGLecture on black boradWe consider measurement-based quantum computation (MBQC) on thermal states of the interacting cluster Hamiltonian containing interactions between the cluster stabilizers that undergoes thermal phase transitions. We show that the long-range order of the symmetry breaking thermal states below a critical temperature drastically enhance the robustness of MBQC against thermal excitations. Specifically, we show the enhancement in two-dimensional cases and prove that MBQC is topologically protected below the critical temperature in three-dimensional cases. The interacting cluster Hamiltonian allows us to perform MBQC even at a temperature an order of magnitude higher than that of the free cluster Hamiltonian.


Nonequilibrium work relation in macroscopic system
Yuki Sughiyama and Masayuki Ohzeki

submitted to J. Stat. Mech.

DSC00828.JPGWhich way do you choose?We reconsider a well-known relationship between the fluctuation theorem and the second law of thermodynamics by evaluating a probability measure-valued process. In order to establish a bridge between microscopic and macroscopic behaviors, we consider the thermodynamic limit of a stochastic dynamical system following the fundamental procedure often used in statistical mechanics. The thermodynamic path characterizing a macroscopic dynamical behavior can be formulated as an infimum of the action functional for the probability measure-valued process. In our formulation, the second law of thermodynamics can be derived by symmetry of the action functional, which is generated from the fluctuation theorem. We find that our formulation not only confirms that the ordinary Jarzynski equality in the thermodynamic limit can be rederived, but also enables us to establish a nontrivial nonequilibrium work relation for metastable states.