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Chihiro Matsui

Publications and source records attributed to Chihiro Matsui.

At least 19 recordsLinked to original sources
arXiv2026

Scar subspaces stabilized by algebraic closure: Beyond equally-spaced spectra and exact solvability

We construct a class of quantum many-body systems hosting an $\mathfrak{su}(3)$-invariant scar subspace, extending the conventional paradigm of quantum many-body scars beyond equally spaced spectra and single-directional tower structures. Our construction is based on local constraints that realize an algebraic closure within the scar subspace. As a result, the spectrum in the subspace is no longer equally spaced, but instead forms a multidirectional lattice structure parametrized by multiple independent quantum numbers. This leads to qualitatively new dynamical signatures: instead of single-frequency revivals, the system exhibits multifrequency oscillations governed by integer linear combinations of distinct energy scales. Importantly, the stability of the scar subspace does not rely on exact solvability of individual eigenstates. We show that algebraic closure preserves the invariant subspace even under perturbations that render the eigenstates analytically intractable, thereby realizing quantum many-body scars on an unsolvable reference state. Our results identify algebraic closure as a unifying mechanism underlying scar subspaces beyond the conventional $\mathfrak{su}(2)$ paradigm, and open a route toward richer nonthermal dynamics in nonintegrable quantum systems.

cond-mat.stat-mech↗
arXiv2025

Symmetry-protected topological scar subspaces

We propose a framework that extends the notion of symmetry-protected topological properties beyond the ground-state paradigm to dynamically isolated subspaces formed by exceptional non-thermal energy eigenstates of non-integrable systems, known as quantum many-body scars (QMBS). We introduce the concept of a symmetry-protected topological (SPT) scar subspace -- a Hilbert subspace stabilized by a restricted spectrum-generating algebra (rSGA) while being protected by on-site, inversion, and time-reversal symmetries. QMBS often admit a non-interacting quasiparticle description, which enables matrix-product representations with small bond dimension. Although individual QMBS do not necessarily retain the protecting symmetries of the Hamiltonian, we show that the subspace formed by the symmetry-connected QMBS does retain them, giving rise to consistently emerging topological properties across the entire scar subspace. Using the spin-$1$ Affleck--Kennedy--Lieb--Tasaki (AKLT) model, we demonstrate that its bimagnon scar subspace reflects the topological properties of the SPT ground state, as evidenced by the appropriate bond-space symmetry representations, the expected topological response, and the numerically verified long-range string order. Our findings indicate that scar subspaces can inherit -- and in inhomogeneous cases systematically modify -- the topological character of the SPT ground state, offering a new and experimentally accessible platform for probing symmetry-protected topology beyond the ground-state regime.

cond-mat.str-el↗
arXiv2025

4T2R X-ReRAM CiM Array for Variation-tolerant, Low-power, Massively Parallel MAC Operation

Computation-in-Memory (CiM) is attracting attention as a technology that can perform MAC calculations required for AI accelerators, at high speed with low power consumption. However, there is a problem regarding power consumption and device-derived errors that increase as row parallelism increases. In this paper, a 4T2R ReRAM cell and an 8T SRAM CiM suitable for CiM is proposed. It is shown that adopting the proposed 4T2R ReRAM cell reduces the errors due to variation in ReRAM devices compared to conventional 4T4R ReRAM cells.

cs.AR↗
arXiv2024

Weak ergodicity breaking with isolated integrable sectors

We consider spin chain models with local Hamiltonians that display weak ergodicity breaking. In these models, the majority of the eigenstates are thermal, but there is a distinguished subspace of the Hilbert space in which ergodicity is broken. We achieve such a weak breaking by embedding selected integrable models into larger Hilbert spaces of otherwise chaotic models. The integrable subspaces do not have a tensor product structure with respect to any spatial bipartition, therefore our constructions differ from certain trivial embeddings. We consider multiple mechanisms for such an embedding, and we also review previous examples in the literature. Curiously, all our examples can be seen as perturbations of models with Hilbert space fragmentation, such that the perturbed models are not fragmented anymore.

cond-mat.stat-mech↗
arXiv2024

Boundary dissipative spin chains with partial solvability inherited from system Hamiltonians

Partial solvability plays an important role in the context of statistical mechanics, since it has turned out to be closely related to the emergence of quantum many-body scar states, i.e., exceptional energy eigenstates which do not obey the strong version of the eigenstate themalization hypothesis. We show that partial solvability of a quantum many-body system can be maintained even when the system is coupled to boundary dissipators under certain conditions. We propose two mechanisms that support partially solvable structures in boundary dissipative systems: The first one is based on the restricted spectrum generating algebra, while the second one is based on the Hilbert space fragmentation. From these structures, we derive exact eigenmodes of the Gorini-Kossakowski-Sudarshan-Lindblad equation for a family of quantum spin chain models with boundary dissipators, where we find various intriguing phenomena arising from the partial solvability of the open quantum systems, including persistent oscillations (quantum synchronization) and the existence of the matrix product operator symmetry. We discuss how the presence of solvable eigenmodes affects long-time behaviors of observables in boundary dissipative spin chains based on numerical simulations using the quantum trajectory method.

cond-mat.stat-mech↗
arXiv2024

Exact steady states of the impurity-doped XXZ spin chain coupled to dissipators

We give an exact matrix product steady state and matrix product forms of local observables for the bulk impurity-doped XXZ spin model coupled to dissipators at both ends, whose dynamics is described by the Lindblad quantum master equation. We find that local magnetization is induced at the impurity site when the spin current flows, which is contrary to the usual situation where current suppresses magnetization due to heating. It is proved that this current-induced magnetization survives in the thermodynamic limit, and the spin current does not depend on the impurity strength. We discuss the role of bulk integrability by comparing the results with those of non-integrable models solved numerically by the quantum trajectory method.

cond-mat.stat-mech↗
arXiv2024

Exactly solvable subspaces of non-integrable spin chains with boundaries and quasiparticle interactions

We propose two new strategies to construct a family of non-integrable spin chains with exactly solvable subspace based on the idea of quasiparticle excitations from the matrix product vacuum state. The first one allows the boundary generalization, while the second one makes it possible to construct the solvable subspace with interacting quasiparticles. Each generalization is realized by removing the assumption made in the conventional method, which is the frustration-free condition or the local orthogonality, respectively. We found that the structure of embedded equally-spaced energy spectrum is not violated by the diagonal boundaries, as log as quasiparticles are non-interacting in the invariant subspace. On the other hand, we show that there exists a one-parameter family of non-integrable Hamiltonians which show perfectly embedded energy spectrum of the integrable spin chain. Surprisingly, the embedded energy spectrum does change by varying the free parameter of the Hamiltonian. The constructed eigenstates in the solvable subspace are the candidates of quantum many-body scar states, as they show up in the middle of the energy spectrum and have entanglement entropies expected to obey the sub-volume law.

cond-mat.stat-mech↗
arXiv2020

Nonequilibrium physics in integrable systems and spin-flip non-invariant conserved quantities

Recently found spin-flip non-invariant (SFNI) conserved quantities play important roles in discussing nonequilibrium physics of the XXZ model. The representative examples are the generalized Gibbs ensemble (GGE) and the ballistic transport of the spin current. In spite of big progress in understanding nonequilibrium physics of integrable systems, the general framework to determine a minimal complete set of conserved quantities which describes the long-time steady state has not yet been found. This paper shows that the GGE of the gapless XXZ model consists of functionally independent conserved quantities rather than linearly independent. At the same time, the physical meaning of SFNI conserved quantities is provided. We also discuss that there exist ballistic channels of the spin current supported by non-quasilocal conserved quantities. The saturation of the lower bound for the Drude weight by quasilocal conserved quantities reads the linear dependence of non-quasilocal conserved quantities on quasilocal ones. We show that their (generalized) linearly dependence relation is consistent with the statement that the GGE consists of functionally independent conserved quantities without containing all linearly independent conserved quantities.

cond-mat.stat-mech↗
arXiv2017

Construction of the steady state density matrix and quasilocal charges for the spin-1/2 XXZ chain with boundary magnetic fields

We construct the nonequilibrium steady state (NESS) density operator of the spin-1/2 XXZ chain with non-diagonal boundary magnetic fields coupled to boundary dissipators. The Markovian boundary dis- sipation is found with which the NESS density operator is expressed in terms of the product of the Lax operators by relating the dissipation parameters to the boundary parameters of the spin chain. The NESS density operator can be expressed in terms of a non-Hermitian transfer operator (NHTO) which forms a commuting family of quasilocal charges. The optimization of the Mazur bound for the high temperature Drude weight is discussed by using the quasilocal charges and the conventional local charges constructed through the Bethe ansatz.

cond-mat.stat-mech↗
arXiv2016

Spinon excitations in the spin-1 XXZ chain and hidden supersymmetry

We study spinon excitations of the integrable spin-1 (Fateev-Zamolodchikov; FZ) chain and their relation to the hidden supersymmetry. Using the notion of the supercharges earlier introduced to the spin chains, which change the system length by one, we found that they nontrivially act on one of two kinds of the degrees of freedom for the FZ chain. Their actions were obtained to be the same as those of the supercharges defined on the supersymmetric sine-Gordon model, the low-energy effective field theory of the FZ chain. Moreover, we construct the eigenstates which are invariant under the supersymmetric Hamiltonian given as the anti-commutator of the supercharges.

cond-mat.stat-mech↗
arXiv2016

Phase coexistence phenomena in an extreme case of the misanthrope process with open boundaries

The misanthrope process is a class of stochastic interacting particle systems, generalizing the simple exclusion process. It allows each site of the lattice to accommodate more than one particle. We consider a special case of the one dimensional misanthrope process whose probability distribution is completely equivalent to the ordinary simple exclusion process under the periodic boundary condition. By imposing open boundaries, high- and low-density domains can coexist in the system, which we investigate by Monte Carlo simulations. We examine finite-size corrections of density profiles and correlation functions, when the jump rule for particles is symmetric. Moreover, we study properties of delocalized and localized shocks in the case of the totally asymmetric jump rule. The localized shock slowly moves to its stable position in the bulk.

nlin.CG↗
arXiv2015

Dynamical supersymmetry on the XXX spin chain

We show the XXX model has the N = 2 dynamical supersymmetry. Using the supercharges defined by the Jordan-Wigner fermions, it was found that the anti-commutation relation of the supercharges gives the Hamiltonian of the XXX model with magnetic field. In order to compare the length-change supercharges with the conventional ones, we interpreted their actions in the spinon basis. In the last part of this paper, we propose the application of the dynamical supersymmetry to the models with magnetic impurities through the Bethe-ansatz analysis.

cond-mat.stat-mech↗
arXiv2014

Boundary effects on the lattice/continuum correspondence: the spin-1/2 XXZ chain and the sine-Gordon model

We derived the corresponding boundary condition on Fermi fields to the spin-1/2 Heisenberg chain with boundary magnetic fields. In order to obtain the correct boundary condition from the variation of the action at the edges, we carefully treat the oscillating terms which emerge as a result of the chiral decomposition of fermions and do not contribute to the bulk Lagrangian. The obtained result is checked by compared with the exact result derived from the Bethe ansatz, by considering the mode expansion of fermions on the light-cone coordinates. We also give the spin-wave interpretation to the emergence of boundary bound states.

cond-mat.stat-mech↗
arXiv2014

Multi-state asymmetric simple exclusion processes

It is known that the Markov matrix of the asymmetric simple exclusion process (ASEP) is invariant under the Uq(sl2) algebra. This is the result of the fact that the Markov matrix of the ASEP coincides with the generator of the Temperley-Lieb (TL) algebra, the dual algebra of the Uq(sl2) algebra. Various types of algebraic extensions have been considered for the ASEP. In this paper, we considered the multi-state extension of the ASEP, by allowing more than two particles to occupy the same box. We constructed the Markov matrix by dimensionally extending the TL generators and derived explicit forms of the particle densities and the currents on the steady states. Then we showed how decay lengths differ from the original two-state ASEP under the closed boundary conditions.

cond-mat.stat-mech↗
arXiv2014

A power-law decay model with autocorrelation for posting data to social networking services

We propose a power-law decay model with autocorrelation for posting data to social networking services concerning particular events such as national holidays or major sport events. In these kinds of events we observe people's interest both before and after the events. In our model the number of postings has a Poisson distribution whose expected value decays as a power law. Our model also incorporates autocorrelations by autoregressive specification of the expected value. We show that our proposed model well fits the data from social networking services.

math.ST↗
arXiv2014

Boundary effects on the supersymmetric sine-Gordon model through light-cone lattice approach

We discussed subspaces of the N=1 supersymmetric sine-Gordon model with Dirichlet boundaries through light-cone lattice regularization. In this paper, we showed, unlike the periodic boundary case, both of Neveu-Schwarz (NS) and Ramond (R) sectors of a superconformal field theory were obtained. Using a method of nonlinear integral equations for auxiliary functions defined by eigenvalues of transfer matrices, we found that an excitation state with an odd number of particles is allowed for a certain value of a boundary parameter even on a system consisting of an even number of sites. In a small-volume limit where conformal invariance shows up in the theory, we derived conformal dimensions of states constructed through the lattice-regularized theory. The result shows existence of the R sector, which cannot be obtained from the periodic system, while a winding number is restricted to an integer or a half-integer depending on boundary parameters.

hep-th↗
arXiv2012

Boundary bound states in the SUSY sine-Gordon model with Dirichlet boundary conditions

We analyze the ground state structure of the supersymmetric sine-Gordon model via the lattice regularization. The nonlinear integral equations are derived for any values of the boundary parameters by the analytic continuation and showed three different forms depending on the boundary parameters. We discuss the state that each set of the nonlinear integral equations characterizes in the absence of source terms. Four different pictures of the ground state are found by numerically studying the positions of zeros in the auxiliary functions. We suggest the existence of two classes in the SUSY sine-Gordon model, which cannot be mixed each other.

hep-th↗