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Hajime Moriya

Publications and source records attributed to Hajime Moriya.

At least 19 recordsLinked to original sources
arXiv2025

Mutual entropy and thermal area law in C*-algebraic quantum lattice systems

We present a general definition of quantum mutual entropy for infinitely extended quantum spin and fermion lattice systems. Using this, we establish a thermal area law in these infinitely extended quantum systems. The proof is based on the local thermodynamical stability (LTS), a variational principle in terms of the conditional free energy. Our thermal area law in quasi-local C*-systems applies to general interactions with well-defined surface energies. We also examine the quantum mutual entropy between the left- and right-sided infinite regions of one-dimensional lattice systems. For general translation-invariant finite-range interactions on such systems, the thermal equilibrium state at any temperature exhibits a finite mutual entropy between these infinite disjoint regions. This further implies that the infinitely large quantum entanglement characteristic of critical ground states in one-dimensional systems is drastically destroyed by even a small positive temperature.

math-ph↗
arXiv2025

Polaronic neutron in dilute alpha matter: A $p$-wave Bose polaron

We theoretically investigate quasiparticle properties of a neutron immersed in an alpha condensate, which is one of the possible states of dilute symmetric nuclear matter. The resonant $p$-wave neutron-alpha scattering, which plays a crucial role in forming halo nuclei, is considered. This system is similar to a Bose polaron near the $p$-wave Feshbach resonance that can be realized in cold-atomic experiments. Calculating the self-energy within the field-theoretical approach, we give an analytical formula for the effective mass of a polaronic neutron as a function of alpha condensation density. Moreover, two adjacent neutrons in a medium, each of which behaves like a stable polaron having an enhanced effective mass, can form a bound dineutron, with the help of $^1S_0$ neutron-neutron attraction. This is in contrast to the case of the vacuum, where a dineutron is known to be unbound. Our result would be useful for understanding many-body physics in astrophysical environments as well as the formation of multi-nucleon clusters in neutron-halo nuclei.

nucl-th↗
arXiv2023

Intersections of ultracold atomic polarons and nuclear clusters: How is a chart of nuclides modified in dilute neutron matter?

Neutron star observations, as well as experiments on neutron-rich nuclei, used to motivate one to look at degenerate nuclear matter from its extreme, namely, pure neutron matter. As an important next step, impurities and clusters in dilute neutron matter have attracted special attention. In this paper, we review in-medium properties of these objects on the basis of the physics of polarons, which have been recently realized in ultracold atomic experiments. We discuss how such atomic and nuclear systems are related to each other in terms of polarons. In addition to the interdisciplinary understanding of in-medium nuclear clusters, it is shown that the quasiparticle energy of a single proton in neutron matter is associated with the symmetry energy, implying a novel route toward the nuclear equation of state from the neutron-rich side.

nucl-th↗
arXiv2023

Nonexistence of spontaneous symmetry breakdown of time-translation symmetry on general quantum systems: Any macroscopic order parameter moves not!

This review informs that the impossibility of genuine quantum time crystals has been known in the C*-algebraic quantum statistical mechanics since 1970s. The KMS condition implies that spontaneous breakdown of time-translation symmetry is impossible in general quantum systems. In particular, any non-trivial order, such as periodic, quasi-periodic, and chaotic order cannot exist in the time direction of equilibrium states, meaning that genuine quantum time crystals are excluded from the outset.

math-ph↗
arXiv2023

Polaronic Proton and Diproton Clustering in Neutron-Rich Matter

We show that strong spin-triplet neutron-proton interaction causes polaronic protons to occur in neutron matter at subnuclear densities and nonzero temperature. As the neutron density increases, proton spectra exhibit a smooth crossover from a bare impurity to a repulsive polaron branch; this branch coexists with an attractive polaron branch. With the neutron density increased further, the attractive polarons become stable with respect to deuteron formation. For two adjacent protons, we find that the polaron effects and the neutron-mediated attraction are sufficient to induce a bound diproton, which leads possibly to diproton formation in the surface region of neutron-rich nuclei in laboratories as well as in neutron stars.

nucl-th↗
arXiv2022

Resonance-to-bound transition of $^5$He in neutron matter and its analogy with heteronuclear Feshbach molecule

We theoretically investigate the fate of a neutron-alpha $p$-wave resonance in dilute neutron matter, which may be encountered in neutron stars and supernova explosions. While $^5$He is known as a resonant state that decays to a neutron and an alpha particle in vacuum, this unstable state turns into a stable bound state in the neutron Fermi sea because the decay process is forbidden by the Pauli-blocking effect of neutrons. Such a resonance-to-bound transition assisted by the Pauli-blocking effect can be realized in cold atomic experiments for a quantum mixture near the heteronuclear Feshbach resonance.

nucl-th↗
arXiv2022

Gibbs variational formula for thermal equilibrium states in terms of quantum relative entropy density

We prove the Gibbs variational formula in terms of quantum relative entropy density that characterizes translation invariant thermal equilibrium states in quantum lattice systems. It is a natural quantum extension of the similar statement established by Föllmer for classical systems. In this work we advocate the viewpoint: Avoid the unique-phase assumption if it is not essential.

math-ph↗
arXiv2022

On quasi-free dynamics on the resolvent algebra

The resolvent algebra is a new C*-algebra of the canonical commutation relations of a boson field given by Buchholz-Grundling. We study analytic properties of quasi-free dynamics on the resolvent algebra. Subsequently we consider a supersymmetric quasi-free dynamics on the graded C*-algebra made of a Clifford (fermion) algebra and a resolvent (boson) algebra. We establish an infinitesimal supersymmetry formula upon the GNS Hilbert space for any regular state satisfying some mild requirement which is standard in quantum field theory. We assert that the supersymmetric dynamics is given as a C*-dynamics.

math-ph↗
arXiv2020

On the open Dicke-type model generated by an infinite-component vector spin

We consider an open Dicke model comprising a single infinite-component vector spin and a single-mode harmonic oscillator which are connected by Jaynes--Cummings-type interaction between them. This open quantum model is referred to as the OISD (Open Infinite-component Spin Dicke) model. The algebraic structure of the OISD Liouvillian is studied in terms of superoperators acting on the space of density matrices. An explicit invertible superoperator (precisely, a completely positive trace-preserving map) is obtained that transforms the OISD Liouvillian into a sum of two independent Liouvillians, one generated by a dressed spin only, the other generated by a dressed harmonic oscillator only. The time evolution generated by the OISD Liouvillian is shown to be asymptotically equivalent to that generated by an adjusted decoupled Liouvillian with some synchronized frequencies of the spin and the harmonic oscillator. This asymptotic equivalence implies that the time evolution of the OISD model dissipates completely in the presence of any (tiny) dissipation.

quant-ph↗
arXiv2018

Ergodicity breaking and Localization of the Nicolai supersymmetric fermion lattice model

We investigate dynamics of the supersymmetric fermion lattice model defined by Hermann Nicolai. We provide its local fermionic constants of motion that exist infinitely many. These generate hidden local supersymmetries that the Nicolai model possesses in addition to its defining dynamical supersymmetry. The existence of such local constants directly implies the breaking ergodicity of the model in the sense of Mazur. At zero temperature, there are infinitely many degenerated classical ground states. We discuss these MBL-like properties. First, we show the delocalization scenario proposed by De Roeck-Huveneers can not naively apply to the Nicolai model at zero temperature despite its disorder-free translation-invariant quantum interaction. Second, we discuss the quantum integrability of the Nicolai model based on the proposal by Caux-Mossel.

math-ph↗
arXiv2018

Supersymmetry breakdown for an extended version of the Nicolai supersymmetric fermion lattice model

Sannomiya-Katsura-Nakayama have recently studied supersymmetry breakdown for an extension of the Nicolai supersymmetric fermion lattice model. This model called the extended Nicolai model is parameterized by an adjustable constant $g\in \mathbb{R}$ in its defining supercharge, and satisfies ${\cal{N}}=2$ supersymmetry. We show that for any non-zero $g$ the extended Nicolai model breaks supersymmetry dynamically, and the energy density of any homogeneous ground state (that breaks supersymmetry) is strictly positive.

math-ph↗
arXiv2015

On supersymmetric fermion lattice systems

We provide a mathematically rigorous framework for supersymmetric fermion lattice systems. We construct supersymmetric C*-dynamics in terms of a nilpotent superderivation and a one-parameter group of automorphisms on the CAR-algebra. (We do not make use of Grassmann numbers.) We establish several basic properties of superderivations on the fermion lattice system. Among others, we obtain a criterion of superderivations to yield supersymmetic dynamics.

math-ph↗
arXiv2006

On fermion grading symmetry

We consider the univalence superselection rule. One would say perhaps ``There is no indication in nature to invalidate this rule. Fermions do not condensate!'' To explain our motivation, let us recall the correspondence of fermion systems and Pauli systems by the Jordan-Wigner transformation. For a finite lattice, fermion grading symmetry corresponds to the Pauli grading. For an infinite lattice, the Pauli-grading can be spontaneously broken e.g. for the XY-model. What is the status of the fermion grading? Nature tells that fermion grading symmmetry cannot be broken for any physical model. But it seems that its rigorous support is needed.

math-ph↗
arXiv2006

Markov property and strong additivity of von Neumann entropy for graded quantum systems

It is easy to verify the equivalence of the quantum Markov property and the strong additivity of entropy for graded quantum systems as well. However, the structure of Markov states for graded systems is different from that for tensor product systems. For three-composed graded systems there are U(1)-gauge invariant Markov states whose restriction to the pair of marginal subsystems is non-separable.

quant-ph↗