論文 - 早田　智也

Phase transition on superfluid vortices in Higgs-Confinement crossover

Hayata T., Hidaka Y., Kondo D.

Journal of High Energy Physics 2025 （ 3 ）  2025年03月

　概要を見る

We propose a novel method to distinguish states of matter by identifying spontaneous symmetry breaking on extended objects, such as vortices, even in the absence of a bulk phase transition. As a specific example, we investigate the phase transition on superfluid vortices in the Higgs-confinement crossover using a U(1)gauge × U(1)global model in (3 + 1) dimensions. This model exhibits superfluidity of U(1)global symmetry and allows for a crossover between the Higgs and confinement regimes by varying the gauge coupling constant from weak to strong. We demonstrate that, on vortices, spontaneous breaking of the ℤ2 flavor symmetry occurs in the weak coupling (Higgs) regime, while it does not in the strong coupling (confinement) regime. We also confirm that those regimes are separated by a second-order phase transition through Monte Carlo simulations, whose universality class corresponds to the two-dimensional Ising model.

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Floquet evolution of the q-deformed SU(3)<inf>1</inf> Yang-Mills theory on a two-leg ladder

Hayata T., Hidaka Y.

Physical Review D 111 （ 3 ）  2025年02月

ISSN  24700010

　概要を見る

We simulate Floquet time evolution of a truncated SU(3) lattice Yang-Mills theory on a two-leg ladder geometry under open boundary conditions using IBM's superconducting 156-qubit device ibm_fez. To this end, we derive the quantum spin representation of the lattice Yang-Mills theory and compose a quantum circuit carefully tailored to hardware, reducing the number of controlled-Z gates. Since it is still challenging to simulate Hamiltonian evolution in present noisy quantum processors, we make the step size in the Suzuki-Trotter decomposition very large and simulate thermalization dynamics in Floquet circuit composed of the Suzuki-Trotter evolution. We demonstrate that IBM's Heron quantum processor can simulate, by error mitigation, Floquet thermalization dynamics in a large system consisting of 62 qubits. Our work would be a benchmark for further quantum simulations of lattice gauge theories using real devices.

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Floquet evolution of the -deformed Yang-Mills theory on a two-leg ladder

T Hayata, Y Hidaka

Physical Review D 111 (3), 034513 2025年

Floquet prethermalization of Z2 lattice gauge theory on superconducting qubits

Hayata T., Seki K., Yamamoto A.

Physical Review D 110 （ 11 ）  2024年12月

筆頭著者, 責任著者, 査読有り,  ISSN  24700010

　概要を見る

Simulating nonequilibirum dynamics of a quantum many-body system is one of the promising applications of quantum computing. We simulate the time evolution of one-dimensional Z2 lattice gauge theory on IBM's superconducting 156-qubit device, ibm_fez. We consider the Floquet circuit made of the Trotter decomposition of Hamiltonian evolution and focus on its dynamics toward thermalization. Quantum simulation with the help of error mitigation is successful in running the Floquet circuit made of 38 and 116 qubits up to 10 Trotter steps in the best case. This is enough to reach the early stage of prethermalization. Our work would be a benchmark for the potential power of quantum computing for high-energy physics problems.

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Chiral fermion on quantum computers

Yamamoto A., Hayata T., Nakayama K.

Proceedings of Science 453 2024年11月

ISSN  23318422

　概要を見る

Quantum computation often suffers from artificial symmetry breaking. We should strive to suppress the artifact both by theoretical and technological improvements. The theoretical formalism of the lattice fermion with exact chiral symmetry is called the chiral fermion. In this presentation, we show how the chiral fermion describes chiral physics in quantum computing. We also show that, although a drawback of the chiral fermion is large computational cost, there is a loophole in one dimension.

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Dense QCD<inf>2</inf> with matrix product states

Hayata T., Hidaka Y., Nishimura K.

Journal of High Energy Physics （Springer Science and Business Media LLC）  2024 （ 7 ）  2024年07月

査読有り,  ISSN  10298479

　概要を見る

We study one-flavor SU(2) and SU(3) lattice QCD in (1 + 1) dimensions at zero temperature and finite density using matrix product states and the density matrix renormalization group. We compute physical observables such as the equation of state, chiral condensate, and quark distribution function as functions of the baryon number density. As a physical implication, we discuss the inhomogeneous phase at nonzero baryon density, where the chiral condensate is inhomogeneous, and baryons form a crystal. We also discuss how the dynamical degrees of freedom change from hadrons to quarks through the formation of quark Fermi seas.

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Non-Hermitian p -wave superfluid and effects of the inelastic three-body loss in a one-dimensional spin-polarized Fermi gas

Tajima H., Sekino Y., Inotani D., Dohi A., Nagataki S., Hayata T.

Physical Review Research 6 （ 2 ）  2024年04月

査読有り,  ISSN  26431564

　概要を見る

We theoretically investigate non-Hermitian p-wave Fermi superfluidity in one-dimensional spin-polarized Fermi gases which is relevant to recent ultracold atomic experiments. Considering an imaginary atom-dimer coupling responsible for the three-body recombination process in the Lindblad formalism, we discuss the stability of the superfluid state against the atomic loss effect. Within the two-channel non-Hermitian BCS-Eagles-Leggett theory, the atomic loss is characterized by the product of the imaginary atom-dimer coupling and the p-wave effective range. Our results indicate that for a given imaginary atom-dimer coupling, a smaller magnitude of the effective ranges of p-wave interaction is crucial for reaching the non-Hermitian p-wave Fermi superfluid state. Moreover, our theoretical framework for many-body systems with the three-body loss, which is inevitable in ultracold atoms, would promote further progress in non-Hermitian cold-atomic physics.

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Two-dimensional lattice with an imaginary magnetic field

Ozawa T., Hayata T.

Physical Review B （American Physical Society (APS)）  109 （ 8 ）  2024年02月

査読有り,  ISSN  24699950

　概要を見る

We introduce a two-dimensional non-Hermitian lattice model with an imaginary magnetic field and elucidate various unique features which are absent in Hermitian lattice models with real magnetic fields. To describe the imaginary magnetic field, we consider both the Landau gauge and the symmetric gauge, which are related by a generalized gauge transformation, changing not only the phase but also the amplitude of the wave function. We discuss the complex energy spectrum and the non-Hermitian Aharonov-Bohm effect as examples of properties which are due to the imaginary magnetic field independent of the generalized gauge transformation. We show that the energy spectrum does not converge as the lattice size is made larger, which comes from the intrinsic nonperiodicity of the model. However, we have found that the energy spectrum does converge if one fixes the length of one side and makes the other side longer; this asymptotic behavior can be understood in the framework of the non-Bloch band theory. We also find an analog of the Aharonov-Bohm effect; the net change of the norm of the wave function upon adiabatically forming a closed path is determined by the imaginary magnetic flux enclosed by the path, which provides an experimentally observable feature of the imaginary magnetic field.

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Dynamical chirality production in one dimension

Hayata T., Nakayama K., Yamamoto A.

Physical Review D 109 （ 3 ）  2024年02月

査読有り,  ISSN  24700010

　概要を見る

We discuss the quantum computation of dynamical chirality production in lattice gauge theory. Although the chirality of a lattice fermion is complicated in general dimensions, it can be simply formulated on a one-dimensional lattice. The chiral fermion formalism enables us to extract the physical part of the chirality production that would be interpreted as the chiral anomaly in the continuous theory. We demonstrate the computation of the Z2 lattice gauge theory on a classical emulator.

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Non-Hermitian -wave superfluid and effects of the inelastic three-body loss in a one-dimensional spin-polarized Fermi gas

H Tajima, Y Sekino, D Inotani, A Dohi, S Nagataki, T Hayata

Physical Review Research 6 (2), 023060 2024年

Floquet prethermalization of Z₂ lattice gauge theory on superconducting qubits

Hayata, T. and Seki, K. and Yamamoto, A.

arXiv 2024年

ISSN  23318422

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Floquet prethermalization of lattice gauge theory on superconducting qubits

T Hayata, K Seki, A Yamamoto

Physical Review D 110 (11), 114503 2024年

q deformed formulation of Hamiltonian SU(3) Yang-Mills theory

Hayata T., Hidaka Y.

Journal of High Energy Physics 2023 （ 9 ）  2023年09月

査読有り,  ISSN  1029-8479

　概要を見る

We study SU(3) Yang-Mills theory in (2 + 1) dimensions based on networks of Wilson lines. With the help of the q deformation, networks respect the (discretized) SU(3) gauge symmetry as a quantum group, i.e., SU(3) k, and may enable implementations of SU(3) Yang-Mills theory in quantum and classical algorithms by referring to those of the stringnet model. As a demonstration, we perform a mean-field computation of the groundstate of SU(3) k Yang-Mills theory, which is in good agreement with the conventional Monte Carlo simulation by taking sufficiently large k. The variational ansatz of the mean-field computation can be represented by the tensor networks called infinite projected entangled pair states. The success of the mean-field computation indicates that the essential features of Yang-Mills theory are well described by tensor networks, so that they may be useful in numerical simulations of Yang-Mills theory.

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String-net formulation of Hamiltonian lattice Yang-Mills theories and quantum many-body scars in a nonabelian gauge theory

Hayata T., Hidaka Y.

Journal of High Energy Physics 2023 （ 9 ）  2023年09月

査読有り,  ISSN  1029-8479

　概要を見る

We study the Hamiltonian lattice Yang-Mills theory based on spin networks that provide a useful basis to represent the physical states satisfying the Gauss law constraints. We focus on SU(2) Yang-Mills theory in (2 + 1) dimensions. Following the string-net model, we introduce a regularization of the Kogut-Susskind Hamiltonian of lattice Yang-Mills theory based on the q deformation, which respects the (discretized) SU(2) gauge symmetry as quantum group, i.e., SU(2)k, and enables implementation of the lattice Yang-Mills theory both in classical and quantum algorithms by referring to those of the string-net model. Using the regularized Hamiltonian, we study quantum scars in a nonabelian gauge theory. Quantum scars are nonthermal energy eigenstates arising in the constrained quantum many-body systems. We find that quantum scars from zero modes, which have been found in abelian gauge theories arise even in a nonabelian gauge theory. We also show the spectrum of a single-plaquette model for SU(2)k and SU(3)k with naive cutoff and that based on the q-deformation to discuss cutoff dependence of the formulation.

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Chiral fermion in the Hamiltonian lattice gauge theory

Hayata T., Nakayama K., Yamamoto A.

Physical Review D 108 （ 3 ）  2023年08月

査読有り,  ISSN  24700010

　概要を見る

We discuss the chiral fermion in the Hamiltonian formalism of lattice gauge theory. Although the naive chiral charge operator does not commute with the Hamiltonian, the commutable one can be defined for the overlap fermion. The eigenvalues of the energy and the chiral charge can be defined simultaneously. We study how the eigenvalue spectrum reflects chiral properties of systems, such as a chiral chemical potential and the axial anomaly. We also show that the Wilson fermion is a chiral fermion in one dimension.

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Non-Hermitian topological Fermi superfluid near the p-wave unitary limit

Tajima H., Sekino Y., Inotani D., Dohi A., Nagataki S., Hayata T.

Physical Review A （AMER PHYSICAL SOC）  107 （ 3 ）  2023年03月

査読有り,  ISSN  24699926

　概要を見る

We discuss theoretically the non-Hermitian superfluid phase transition in one-dimensional two-component Fermi gases near the p-wave Feshbach resonance accompanied by the two-body loss associated with dipolar relaxation. We point out that this system gives us an opportunity to explore the interplay among various nontrivial properties such as universal thermodynamics at divergent p-wave scattering lengths, the topological phase transition at vanishing chemical potential, and the non-Hermitian Bardeen-Cooper-Schrieffer (BCS) to Bose-Einstein condensate (BEC) transition, in a unified manner. In the BCS phase, the loss-induced superfluid-normal transition occurs when the exceptional point appears in the effective non-Hermitian Hamiltonian. In the BEC phase, the diffusive gapless mode can be regarded as a precursor of the instability of the superfluid state. Moreover, we show that the superfluid state is fragile against the two-body loss near the topological phase transition point.

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Dissipation-induced dynamical phase transition in postselected quantum trajectories

Hayata T., Hidaka Y., Yamamoto A.

Progress of Theoretical and Experimental Physics （OXFORD UNIV PRESS INC）  2023 （ 2 ）  2023年02月

査読有り,  ISSN  2050-3911

　概要を見る

It is known that effects of dissipation or measurement backreaction in postselected quantum trajectories are described by a non-Hermitian Hamiltonian, but their consequences in real-time dynamics of many-body systems are yet to be elucidated. Through a study of a non-Hermitian Hubbard model, we reveal a novel dissipation-induced dynamical phase transition in postselected quantum trajectories, where time controls the strength of postselection and becomes the intrinsic parameter inducing the phase transition. Our findings are testable in ultracold atom experiments and may open a new avenue in the dissipative engineering of quantum systems.

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Non-Hermitian topological Fermi superfluid near the -wave unitary limit

H Tajima, Y Sekino, D Inotani, A Dohi, S Nagataki, T Hayata

Physical Review A 107 (3), 033331 2023年

Lattice Lindblad simulation

Hayata T., Hidaka Y., Yamamoto A.

Progress of Theoretical and Experimental Physics （OXFORD UNIV PRESS INC）  2022 （ 5 ）  2022年05月

査読有り,  ISSN  2050-3911

　概要を見る

We perform real-Time lattice simulation of an open quantum system based on the Schwinger-Keldysh path integral representation of the Lindblad formalism. Although the real-Time simulation generally suffers from the sign problem, a few exceptional cases exist. We focus on a sign-problem-free system of a non-relativistic spinless fermion and analyze the time evolution under driving and dissipation.

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Diagnosis of information scrambling from Hamiltonian evolution under decoherence

Hayata T., Hidaka Y., Kikuchi Y.

Physical Review D （AMER PHYSICAL SOC）  104 （ 7 ）  2021年10月

査読有り,  ISSN  24700010

　概要を見る

We apply a quantum teleportation protocol based on the Hayden-Preskill thought experiment to quantify how scrambling a given quantum evolution is. It has an advantage over the direct measurement of out-of-time ordered correlators when used to diagnose the information scrambling in the presence of decoherence effects stemming from a noisy quantum device. We demonstrate the protocol by applying it to two physical systems: Ising spin chain and SU(2) lattice Yang-Mills theory. To this end, we numerically simulate the time evolution of the two theories in the Hamiltonian formalism. The lattice Yang-Mills theory is implemented with a suitable truncation of Hilbert space on the basis of the Kogut-Susskind formalism. On a two-leg ladder geometry and with the lowest nontrivial spin representations, it can be mapped to a spin chain, which we call the Yang-Mills-Ising model and is also directly applicable to future digital quantum simulations. We find that the Yang-Mills-Ising model shows the signal of information scrambling at late times.

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