arXiv subjects

Atsushi Ono

Publications and source records attributed to Atsushi Ono.

At least 19 recordsLinked to original sources

arXiv2026

High-harmonic fingerprints of sharp spin twists in a chiral soliton lattice

A magnetic field applied perpendicular to the helical axis of a monoaxial chiral helimagnet compresses the spin helix into a coplanar chiral soliton lattice (CSL). We show that optically driven high-harmonic generation from itinerant electrons coupled to a frozen CSL resolves the lattice-scale structure of the localized twist, rather than the continuum soliton shape. High-order harmonics remain perturbative for the uniform helix. As the winding localizes at fixed magnetic period, they grow by many orders of magnitude and acquire a nonperturbative dependence on the drive amplitude. The growth originates from a spatially nonuniform effective hopping that turns each soliton into a localized dip in the hopping amplitude. When the degree of winding localization is held fixed, high-order intensities fall by many orders of magnitude as the magnetic period increases toward the continuum limit, where the hopping modulation is spatially smoothed. High-order harmonics thus resolve a real-space characteristic of the coplanar CSL, even in the absence of scalar chirality and an emergent magnetic field.

cond-mat.str-el↗

arXiv2026

Floquet Green's functions for lattice electrons driven by Gaussian quantum light

We formulate Floquet Green's functions for noninteracting single-band lattice electrons driven by a reservoir-stabilized single-mode Gaussian quantum light source. The source is prescribed externally and is not updated by the many-electron polarization, while an active electronic probe still conditions the source evolution through the Peierls coupling. The two time arguments of a Green's function share one source history: the lesser and greater components are obtained by convolving a shared-history four-endpoint kernel with the continuous bath kernels before the final source trace, while the bath canonical anticommutation relation yields an equal-time covariance that seeds the retarded and advanced one-leg propagations. The Peierls coupling is treated nonperturbatively within the prescribed-source model, and classical Floquet theory is recovered in the appropriate limit. Numerical calculations on a minimal one-dimensional model show finite-coupling quantum-source corrections beyond a prescribed classical drive, together with spectral reconstruction and occupancy redistribution for squeezed vacuum and squeezed coherent sources. The squeezing parameter and phase provide additional control knobs, beyond classical amplitude modulation, for both sideband structure and occupied weight. This work provides a theoretical framework for quantum Floquet engineering of condensed matter with an externally prescribed quantum light source.

cond-mat.str-el↗

arXiv2026

Tangent equations of motion for nonlinear response functions

Nonlinear response functions, formulated as multipoint correlation functions or Volterra kernels, encode the dynamical and spectroscopic properties of physical systems and underpin a wide range of nonlinear transport and optical phenomena. However, their evaluation rapidly becomes prohibitive at high orders because of combinatorial (often factorial) scaling or severe numerical errors. Here, we establish a systematic and efficient framework to compute nonlinear response functions directly from real-time dynamics, without explicitly constructing multipoint correlators or relying on numerically unstable finite-difference methods for order-resolved extraction. Our approach is based on the Gateaux derivative with respect to the external field in function space, which yields a closed hierarchy of tangent equations of motion (TEOM). Propagating the TEOM alongside the original dynamics isolates each perturbative order with high accuracy, providing a term-by-term decomposition of physical contributions. The computational cost scales exponentially with response order in the fully general setting and reduces to polynomial complexity when all perturbation directions are identical; both regimes avoid the factorial scaling of explicit multipoint-correlator evaluations. We demonstrate the power of TEOM by computing frequency-resolved fifth-order response functions for a solid-state electron model and by obtaining nonlinear response functions up to the 49th order with controlled accuracy in a classical Duffing oscillator. We further show that our time-evolution formulation allows optical conductivities to be evaluated directly while remaining numerically stable even near zero frequency. TEOM can be incorporated seamlessly into existing real-time evolution methods, yielding a general framework for computing nonlinear response functions in quantum and classical dynamical systems.

cond-mat.str-el↗

arXiv2026

Electron dynamics induced by quantum cat-state light

We present an effective theory for describing electron dynamics driven by an optical external field in a Schrödinger's cat state. We show that the reduced electron density matrix evolves as an average over trajectories $\{ρ_α\}$ weighted by the Sudarshan--Glauber $P$ distribution $P(α)$ in the weak light--matter coupling regime. Each trajectory obeys an equation of motion, $\mathrm{i} \partial_tρ_α=\mathcal{H}_α ρ_α-ρ_α\mathcal{H}_α$, where an effective Hamiltonian $\mathcal{H}_α$ becomes non-Hermitian due to quantum interference of light. The optical quantum interference is transferred to electrons through the asymmetric action between the ket and bra state vectors in $ρ_α$. This non-Hermitian dynamics differs from the conventional one observed in open quantum systems, described by $\mathrm{i} \partial_tρ=\mathcal{H}ρ-ρ\mathcal{H}^\dagger$, which has complex conjugation in the second term. We confirm that the reduced, trajectory-resolved effective theory agrees with full electron-photon simulations for the few-electron Dicke model, thereby validating the interferential non-Hermitian description in the weak-coupling regime.

quant-ph↗

arXiv2025

Temporal modulation of second harmonic generation in ferroelectrics by a pulsed electric field

We revisit the relationship between electric polarization modulation $ΔP$ in ferroelectrics induced by a low-frequency pulsed electric field and the corresponding second harmonic intensity modulation $ΔI_{\mathrm{SH}}$. Using nonlinear response theory, we derive their time-domain expressions linear in the pulse amplitude, revealing that not only the electric field but also its time derivative contributes to $ΔI_{\mathrm{SH}}$. Furthermore, even when the time-derivative component is negligible, $ΔI_{\mathrm{SH}}$ can be in antiphase with the pulsed field and thus with $ΔP$. These theoretical predictions are further supported by real-time simulations of a model for electronic ferroelectrics. Our results demonstrate that the commonly assumed relation $ΔP \propto ΔI_{\mathrm{SH}}$ can break down under certain conditions, reflecting the complex-valued and frequency-dependent nature of nonlinear dynamical susceptibilities.

cond-mat.mtrl-sci↗

arXiv2025

Extracting Nonlinear Dynamical Response Functions from Time Evolution

We develop a general framework based on the functional derivative to extract nonlinear dynamical response functions from the temporal evolution of physical quantities, without explicitly computing multipoint correlation functions. We validate our approach by calculating the second- and third-order optical responses in the Rice-Mele model and further apply it to a many-body interacting system using a tensor network method. This framework is broadly applicable to any method that can compute real-time dynamics, offering a powerful and versatile tool for investigating nonlinear responses in dynamical systems.

cond-mat.str-el↗

arXiv2024

Nonlocal correlations in quantum energy teleportation: perspectives from their Majorana representations and information thermodynamics

Motivated by anomalous nonlocal correlation in the Kitaev spin liquids, we propose a quantum energy teleportation protocol between remote partners Alice and Bob on a quantum spin model, and examine how its performance is characterized by Majorana fermions that clearly depict nonlocal correlations inherent in the model. In our model, Bob's energy extraction is activated by local energy injection by Alice's projective measurement and subsequent classical communication of the measurement result. We derive two formulae: one for the maximally extracted energy by the protocol and the other for the maximum of energy reduction at Bob's local site. We find that the extracted energy becomes positive when a nonlocal correlator defined by Majorana fermions at Alice's and Bob's sites is finite. We also find that the amount of the energy reduction becomes positive when another nonlocal Majorana correlator is finite. In both formulae, the correlators appear as a result of Bob's feedback unitary operation. We discuss effective information-thermodynamical aspects behind the protocol at zero temperature.

quant-ph↗

arXiv2024

High harmonic generation from electrons moving in topological spin textures

High harmonic generation (HHG) is a striking phenomenon, which reflects the ultrafast dynamics of electrons. Recently, it has been demonstrated that HHG can be used to reconstruct not only the energy band structure but also the geometric structure characterized by the Berry curvature. Here, we numerically investigate HHG arising from electrons coupled with a topological spin texture in a spin scalar chiral state where time reversal symmetry is broken. In this system, a sign change in scalar chirality alters the sign of the Berry curvature while keeping the energy band structure unchanged, allowing us to discuss purely geometrical effects on HHG. Notably, we found that, when the optical frequency is significantly lower than the energy gap, the sign of scalar chirality largely affects the longitudinal response parallel to the optical field rather than the transverse response. Our analysis suggests that this can be attributed to interband currents induced by the recombination of electron-hole pairs whose real-space trajectories are modulated by the anomalous velocity term.

cond-mat.mes-hall↗

arXiv2024

Real-time control of non-Abelian anyons in Kitaev spin liquid under energy dissipation

Quantum spin liquids realized in the Kitaev model offer a platform for fractionalization of spin into two quasiparticles: itinerant Majoranas and localized visons. Introducing a uniform weak magnetic field associates a Majorana zero mode with each vison excitation. The vison accompanied by a Majorana zero mode is known to behave as a non-Abelian anyon, which has garnered significant attention for its potential applications in topological quantum computing. Although spatial and temporal control of these anyons is essential for exploring their applicability in quantum computing, numerical simulations of creating, moving, and annihilating anyons by an external field remain challenging as this field violates the exact solvability of the Kitaev model. Moreover, such a field to control anyons may disturb the quantum state due to the energy injection it causes. In this study, by introducing energy dissipation phenomenologically in real-time simulations, we demonstrate that the generation, movement, and annihilation of vison excitations can be achieved while maintaining their localization. We find that a vison can be moved in a desired direction by using time-dependent local magnetic fields or gradient fields, and it remains accompanied by a Majorana zero mode even after its movement. We also reveal that a larger spatial extent of the Majorana zero modes bound to a vison facilitates the movement of the vison with smaller field gradients. Furthermore, our numerical simulations demonstrate pair creation and annihilation of visons, triggered by time-dependent magnetic fields. The results obtained in this study highlight the significance of energy dissipation in controlling non-Abelian anyons, which will stimulate further investigations into the nonequilibrium dynamics of fractional quasiparticles in strongly correlated electron systems, as well as studies for applications in quantum computation.

cond-mat.str-el↗

arXiv2023

Field-driven spatiotemporal manipulation of Majorana zero modes in a Kitaev spin liquid

The Kitaev quantum spin liquid possesses two fractional quasiparticles, itinerant Majorana fermions and localized visons. It provides a promising platform for realizing a Majorana zero mode trapped by a vison excitation. This local mode behaves as a non-Abelian anyon capable of applications to quantum computation. However, creating, observing, and manipulating visons remain challenging even in the pristine Kitaev model. Here, we propose a theory to control visons enabled by a time-dependent local magnetic field in the Kitaev spin liquid. Examining the time evolution of the magnetic state, we demonstrate that a vison follows a locally applied field sweeping in the system. We clarify that one can move a vison accompanied by a Majorana zero mode by choosing the velocity and shape of the local field appropriately. In particular, the controllability of visons using local fields shows nonlinear behavior for its strength, which originates from interactions between Majorana fermions and visons. The present results suggest that itinerant Majorana fermions other than zero modes play a crucial role in vison transport. Our finding will offer a guideline for controlling Majorana zero modes in the Kitaev quantum spin liquid.

cond-mat.str-el↗

arXiv2023

Photocontrol of spin scalar chirality in centrosymmetric itinerant magnets

Noncoplanar magnetic structures, such as magnetic skyrmions, are characterized by spin chirality and usually favored by antisymmetric exchange interactions in noncentrosymmetric magnets. Here, we show that a linearly polarized electric-field pulse stabilizes a nonequilibrium spin scalar chiral state in a centrosymmetric itinerant ferromagnet. The scalar chirality has a nonmonotonic dependence on the electric-field strength, and its sign can be controlled by circular polarization. Furthermore, magnetic skyrmions are excited after the pulse decays. A photoinduced nonthermal electron distribution plays an important role for instability towards the spin scalar chiral state as well as the $120^{\circ}$ Néel state, depending on the next-nearest-neighbor transfer integral. These results provide an alternative route to controlling spin chirality by photoirradiation.

cond-mat.str-el↗

arXiv2023

Theory for Fourier-limited attosecond pulse generation in solids

The generation of ultrashort light pulses is essential for the advancement of attosecond science. Here, we show that attosecond pulses approaching the Fourier limit can be generated through optimized optical driving of tunneling particles in solids. We propose an ansatz for the wave function of tunneling electron-hole pairs based on a rigorous expression for massive Dirac fermions, which enables efficient optimization of the waveform of the driving field. It is revealed that the dynamic sign change in the effective mass due to optical driving is crucial for shortening the pulse duration, which highlights a distinctive property of Bloch electrons that is not present in atomic gases, i.e., the periodic nature of crystals. These results show the potential of utilizing solid materials as a source of attosecond pulses.

cond-mat.mes-hall↗

arXiv2022

Energy-band echoes: Time-reversed light emission from optically driven quasiparticle wavepackets

The at-will control of quantum states is a primary goal of quantum science and technology. The celebrated Hahn echo exemplifies such quantum-state control based on a time-reversal process in a few-level system. Here, we propose a different echo phenomenon associated with the energy-band structure in quantum many-body systems. We show that the dynamics of quasiparticle wavepackets can be reversed by a driving electric-field pulse, yielding echoes with the time-reversed waveform of the optical excitation pulse when the quasiparticles recombine. The present echoes are observed not only in band insulators but also in correlated insulators, including a Mott insulator and a spontaneously-broken-symmetry charge-ordered insulator, in one- and higher-dimensional systems, irrespective of the integrability of the models. Analytical expressions reveal the conditions under which the echoes appear, and they also indicate that the frequency of the echo pulses reflects the dispersion relation for quasiparticles such as electron-hole pairs, doublon-holon pairs, and kink-antikink pairs. These findings provide a framework for all-optical momentum-resolved spectroscopy of the quasiparticles in quantum many-body systems.

cond-mat.str-el↗

arXiv2021

Ultrafast reorientation of the Néel vector in antiferromagnetic Dirac semimetals

Antiferromagnets exhibit distinctive characteristics such as ultrafast dynamics and robustness against perturbative fields, thereby attracting considerable interest in fundamental physics and technological applications. Recently, it was revealed that the Néel vector can be switched by a current-induced staggered (Néel) spin-orbit torque in antiferromagnets with the parity-time symmetry, and furthermore, a nonsymmorphic symmetry enables the control of Dirac fermions. However, the real-time dynamics of the magnetic and electronic structures remain largely unexplored. Here, we propose a theory of the ultrafast dynamics in antiferromagnetic Dirac semimetals and show that the Néel vector is rotated in the picosecond timescale by the terahertz-pulse-induced Néel spin-orbit torque and other torques originating from magnetic anisotropies. This reorientation accompanies the modulation of the mass of Dirac fermions and can be observed in real time by the magneto-optical effects. Our results provide a theoretical basis for emerging ultrafast antiferromagnetic spintronics combined with the topological aspects of materials.

cond-mat.mes-hall↗

arXiv2020

Electric-Field-Induced Antiferromagnetic Insulating State in a Metallic Ferromagnet

We show that a static electric field induces the transition from a ferromagnetic metal to an antiferromagnetic insulator owing to the Bloch oscillation of conduction electrons. In the steady state, the electric current is inversely proportional to the applied electric field, implying the nonperturbative insulating nature that is different from the Wannier-Stark localization. Possible experimental realization based on recent terahertz pulse sources is discussed.

cond-mat.str-el↗

arXiv2019

High-Harmonic Generation in a Correlated Electron System

High-harmonic generation (HHG) in crystalline solids have been examined so far on the basis of one-body energy-band structures arising from electron itineracy in a periodic potential. Here, we show emergence of HHG signals which are attributed to dynamics of many-body states in a low-dimensional correlated electron system. An interacting fermion model and its effective pseudo-spin model on a one-dimensional dimer-type lattice are analyzed. Observed HHG signals in a spontaneously symmetry-broken state, where charge densities are polarized inside of dimer units, show threshold behavior with respect to light amplitude and are interpreted in terms of tunneling and recombination of kink-antikink excitations in an electric field.

cond-mat.str-el↗

arXiv2018

Nonequilibrium susceptibility in photoinduced Floquet states

Nonequilibrium susceptibility in photoinduced Floquet states is studied. We analyze an electron system coupled with a heat bath in a time-periodic oscillating electric field. Spin/charge susceptibility is formulated on the basis of the Floquet Green function method, and is calculated numerically in a wide range of amplitude and frequency of light. When the frequency is larger than the bandwidth, the susceptibility is enhanced due to the dynamical localization effect, and their peak positions in the momentum space are shifted by the Fermi surface deformation. In the case of the small frequency and amplitude, multiple-peak structure emerges in the susceptibility, originating from the multiple Floquet bands which cross the Fermi level. To confirm those numerical results and provide the interpretation, an approximated expression of the susceptibility is derived for small electric-field amplitude.

cond-mat.str-el↗

arXiv2018

Photoinduced topological spin texture in a metallic ferromagnet

Photoinduced nonequilibrium spin structure is examined in the double-exchange model, in which itinerant electrons couple with localized spins through the ferromagnetic Hund coupling. In particular, we focus on the transient spin structure from the initial ferromagnetic metallic state to the steady antiferromagnetic ordered state reported in [Phys. Rev. Lett. 119, 207202 (2017)]. By solving the Schrödinger equation combined with the Landau-Lifshitz-Gilbert equation, we find finite winding number and chirality, which implies emergence of topological chiral spin textures. These observations are reproduced by a calculation where spin dynamics after sudden quench of the chemical potential are examined in larger clusters. A possible mechanism of the topological spin texture in the transient dynamics is discussed.

cond-mat.str-el↗