arXiv subjects

Hiroaki Matsueda

Publications and source records attributed to Hiroaki Matsueda.

At least 19 recordsLinked to original sources

arXiv2026

Interference-induced state engineering and Hamiltonian control for noisy collective-spin metrology

Interference provides a fundamental mechanism for generating and manipulating entanglement in many-body quantum systems. Here, we develop an interference framework in which the nonlinear dynamics of collective spin-$\tfrac{1}{2}$ ensembles are mapped onto phase accumulation and self-interference in phase space, providing a direct and physically transparent description of entanglement formation. Within this framework, one-axis twisting produces Greenberger-Horne-Zeilinger (GHZ) states, while two-axis twisting generates multi-component GHZ superpositions relevant for multiparameter quantum metrology. Building on this interference-based description, we analyze metrological performance under realistic Markovian noise, including local and collective emission, pumping, and dephasing, and examine the role of Hamiltonian control based on linear and nonlinear interactions. We show that the optimal control enhances sensitivity in both single- and multiparameter estimation across noise-dependent regimes. These results establish interference as a unifying principle linking nonlinear dynamics, entanglement generation, and metrological performance. This framework offers a broadly applicable route to robust quantum-enhanced sensing in noisy many-body systems.

quant-ph↗

arXiv2026

On Identification of Heat and Work in Quantum Many-Body Systems with Local Operations and Classical Communication

How we identify heat and work is a fundamental question in modern quantum thermodynamics. Usually, heat and work are attributed to changes in the density matrix and the Hamiltonian, respectively, during time-evolution processes in quantum systems. Recently, it has been recognized that this identification is ambiguous. Furthermore, quantum thermodynamics involving quantum measurement is still under development. Motivated by these on-going works, we consider a quantum many-body system from which we extract energy by local operations and classical communication (LOCC) according to the quantum energy teleportation (QET) protocol. The central idea to define heat and work unambiguously is based on a sharp insight into the optimization condition of LOCC. When LOCC is optimized, the extractable energy by QET becomes a daemonic ergotropy; thus, it can be attributed as work. On the other hand, when LOCC is not optimized, we have not squeezed out all the energy with the unitary operation. It means there is uncontrollable energy left in the system. The uncontrollable energy can be attributed as heat after careful treatment of many-body interactions. The heat term consists of nonlocal correlation due to communication between remote participants, and the correlation cannot be directly observed for the participant in the subsystem. Thus, this feature is consistent with the traditional perspective of heat as an uncontrollable energy. To deeply understand the nature of heat, we derive two types of generalized Clausius inequality in our effective quantum thermodynamics, and discuss the direction of the inequality. To justify our perspective, we examine a one-dimensional Kitaev-like model and discuss the physical meaning of effective temperature in our thermodynamics.

quant-ph↗

arXiv2026

Connecting Density Matrix Spectroscopy to Biexciton Entanglement Dynamics

Quantum entanglement is one of the most intriguing features of quantum mechanics. To investigate the entanglement between two excitons in a biexciton, an experimental technique called density matrix spectroscopy (DMS) has recently been developed. DMS combines stimulated emission tomography and pump-probe techniques to obtain a time-resolved density matrix of the polarization state of a photon pair emitted from the biexciton. The reconstructed density matrix is expected to encode information about the biexciton state and its entanglement dynamics, but the precise nature of this connection has remained unclear. In this paper, we derive an analytical relationship between the density matrix obtained by DMS and the biexciton state. In addition, we perform numerical simulations to compare the entanglement dynamics obtained by DMS with the biexciton's entanglement dynamics in a two-dimensional electron-hole system using an extended ionic Hubbard model. We find that DMS can partially capture the entanglement in the biexciton, in particular, the dynamics of the difference $S_{\mathrm{bi}} - S_k$, where $S_{\mathrm{bi}}$ is the entanglement entropy of the biexciton and $S_k$ is the entanglement in terms of the wavevectors of the excitons that constitute the biexciton. These results demonstrate the validity of DMS for obtaining information about the entanglement dynamics of the biexciton.

quant-ph↗

arXiv2026

Continuous Reset-Induced Phase Transition in Measurement-Free Random Quantum Circuits

We study a random unitary quantum circuit with only reset channels, which has high feasibility for real quantum devices. In particular, we investigate the many-body statistical physics properties, "reset-induced" entanglement phase transitions comparing the classical statistical picture in the large "$d$" limit of qudits. In the property of the reset-induced phase transition the parameter of qudit $d$ is essential. That is, the transition properties induced by the reset channel significantly depend on $d$. We numerically elucidate this statement employing efficient stabilizer circuit simulations for $d=2$. Specifically, large fluctuations are observed near the critical point, indicating that the reset-induced phase transition is continuous. We obtain clear data collapses, consistent with a second-order mixed phase transition. This behavior differs from expectations based on the classical statistical mapping in the large-$d$ limit.

quant-ph↗

arXiv2026

Current-control of chaos and effects of thermal fluctuations in magnetic tunnel junctions

We theoretically investigate the chaotic behavior of spin-torque ferromagnetic resonance in magnetic tunnel junctions (MTJs) with perpendicular magnetic anisotropy under thermal fluctuations. By calculating the Lyapunov exponent based on the Landau-Lifshitz-Gilbert equation, we demonstrate that an MTJ characterized by a double-well potential, composed of uniaxial magnetic anisotropy and an external magnetic field, exhibits chaotic magnetization dynamics that can be controlled by means of the DC current bias. Furthermore, we find that thermal fluctuations help to induce these chaotic magnetization dynamics, which can be regarded as noise-induced chaos. This research provides a basis for brain-inspired computing using spintronic devices and advances the understanding of the interplay between thermal fluctuations and chaos in magnetization dynamics.

cond-mat.mes-hall↗

arXiv2025

Trade-off relation between integrated metrological gain and local dissipation in magnetic-field sensing by quantum spin ensemble

Quantum metrology plays a central role in precision sensing, where quantum enhancement of detection performance is crucial for both fundamental studies and practical applications. In this work, we derive a tight performance bound for magnetic-field sensing with a spin ensemble in the presence of dissipation. The metrological performance is quantified by the integrated metrological gain (IMG), which explicitly incorporates the time evolution of the measurement apparatus. By combining the Lindblad master equation with the quantum Fisher information, we obtain analytically exact trade-off relations between the IMG and the dissipation rate for local dephasing and local emission processes, showing that the gain scales inversely with the dissipation strength. This trade-off complements the Heisenberg limit, which addresses only the scaling with the number of spins and neglects dissipative dynamics. We analyze various initial state preparations and elucidate the role of quantum entanglement in the presence of dissipation. Notably, while entanglement is essential for achieving Heisenberg scaling at short times, it also accelerates dissipative degradation during time evolution. Consequently, for sufficiently long observation times, comparable metrological performance can be achieved even without entanglement.

quant-ph↗

arXiv2025

Theoretical analysis of photon detection mechanism in superconducting single-photon detectors

To elucidate the photon detection mechanism of superconducting single-photon detectors, we theoretically examine the dynamics of type-II superconductors with a bias current using the two-dimensional time-dependent Ginzburg-Landau and the Maxwell equations. The photon injection that weakens the superconducting order parameter is treated phenomenologically as a local temperature increase, and the amount of injection is controlled by the initial hotspot radius. The photon is detected by the voltage change between two electrodes attached to the left and right edges of the superconductor. We find that certain parameter ranges can be explained by the traditionally considered hotspot model, while other parameter ranges are governed by the generation and annihilation of superconducting vortex and antivortex pairs. The photon detection is possible for an initial hotspot radius that exceeds a threshold value. We find that the generation of a vortex--antivortex pair occurs near the threshold. The flow of the pair perpendicular to the current direction finally creates a normal region for the photon detection. The voltage change for the Ginzburg--Landau parameter close to the transition point from type-II to type-I superconductor shows anomalous behavior that is not associated with the dynamics of the vortex--antivortex pair. We also examine the effects of spatially non-uniform current density on the voltage change and the superconducting order parameter to provide a hint to understand the behavior of wide-strip single-photon detectors. The estimated values of incident photon energy and response time for photon detection are reasonable in comparison with experiments. The present comprehensive examination provides useful guidelines for flexible design of device structures.

cond-mat.supr-con↗

arXiv2025

Circuit-based cavity magnonics in the ultrastrong and deep-strong coupling regimes

We theoretically study nonperturbative strong-coupling phenomena in cavity magnonics systems in which the uniform magnetization dynamics (magnons) in a ferromagnet is coupled to the microwave magnetic field (photons) of a single LC resonator. Starting from an effective circuit model that accounts for the magnetization dynamics described by the Landau-Lifshitz-Gilbert equation, we show that a nontrivial frequency shift emerges in the ultrastrong and deep-strong coupling regimes, whose microscopic origin remains elusive within a purely classical framework. The circuit model is further quantized to derive a minimal quantum mechanical model for generic cavity magnonics, which corresponds to a two-mode version of the Hopfield Hamiltonian and explains the mechanism of the frequency shifts found in the {\it classical} circuit model. We also formulate the relation between the frequency shift and quantum quantities, such as the ground-state particle number, quantum fluctuations associated with the Heisenberg uncertainty principle, and entanglement entropy, providing a nondestructive means to experimentally access to these quantum resources. By utilizing soft magnons in an anisotropic ferromagnet, we further demonstrate that these quantum quantities diverge at the zeros of the magnon band edges as a function of the external magnetic field. This work paves the way for cavity magnonics beyond the conventional strong coupling regime.

cond-mat.mes-hall↗

arXiv2025

Gain-driven magnon-polariton dynamics in the ultrastrong coupling regime: Effective circuit approach for coherence versus nonlinearity

We theoretically study the dynamics of gain-driven magnon-polaritons (MPs), which characterizes auto-oscillation of MPs, across the strong coupling (SC) and ultrastrong coupling (USC) regimes. Taking into account the magnon dynamics via the magnetic flux, we present an effective circuit model of gain-driven MPs, which allows to manipulate the coupling strength of MPs by tuning the size of a ferromagnet and incorporates the self-Kerr nonlinearity of magnons due to the shape magnetic anisotropy. In the SC regime, we find that the self-Kerr nonlinearity generates a frequency shift and reduces the coherent magnon-photon coupling. In contrast, in the USC regime, we find that the coherent magnon-photon coupling not only overcomes the self-Kerr nonlinearity but also effectively couples to gain via the imaginary part of complex eigenfrequencies, resulting in magnon-like auto-oscillations. Subsequently, the USC enables one to widely tune the auto-oscillation frequency by means of an external magnetic field. These findings indicate that there is a trade-off relation between the coupling strength of MPs and the self-Kerr nonlinearity of magnons. This work is attributed to understanding of the interplay between gain-loss and USC in nonlinear polariton dynamics, offering a novel principle for frequency tunable maser-like devices based on gain-driven MPs.

cond-mat.mes-hall↗

arXiv2025

Disordered purification phase transition in hybrid random circuits

Noise is inevitable in realistic quantum circuits. It arises randomly in space. Inspired by spatial non-uniformity of the noise, we investigate the effects of spatial modulation on purification phase transitions in a hybrid random Clifford circuit. As an efficient observable for extracting quantum entanglement in mixed states, we employ many-body negativity. The behavior of the many-body negativity well characterizes the presence of the purification phase transitions and its criticality. We find the effect of spatial non-uniformity in measurement probability on purification phase transition. The criticality of the purification phase transition changes from that of uniform probability, which is elucidated from the argument of the Harris criterion. The critical correlation length exponent $ν$ changes from $ν< 2$ for uniform probability to $ν> 2$ for spatially modulated probability. We further investigate a setting where two-site random Clifford gate becomes spatially (quasi-)modulated. We find that the modulation induces a phase transition, leading to a different pure phase where a short-range quantum entanglement remains.

quant-ph↗

arXiv2025

Chaotic magnetization dynamics in magnetic Duffing oscillator

We propose a magnetic analogy of the Duffing oscillator--magnetic Duffing oscillator--which is characterized by a double-well magnetic potential of a ferromagnet with a uniaxial magnetic anisotropy. Based on the linear stability analysis of the Landau-Lifshitz-Gilbert equation, we show that an external magnetic field applied perpendicular to the magnetic anisotropy field creates an anharmonicity on the magnetic potential, generating homoclinic orbits in the phase space. By evaluating the Lyapunov exponent, we demonstrate that the magnetic Duffing oscillator exhibits chaotic behaviors in the presence of periodically oscillating external forces: Oersted field and spin-orbit torque by considering the ferromagnet/heavy-metal bilayer. We also show that the external magnetic field can be adjusted to generate or modify homoclinic orbits, thereby controlling the parameter range of the oscillating external forces that induce chaos. This work deepens our understanding of chaotic magnetization dynamics by bridging the fields of nonlinear dynamics and spintronics.

cond-mat.mes-hall↗

arXiv2025

Unconventional Josephson supercurrent diode effect induced by chiral spin-orbit coupling

Chiral materials lacking mirror symmetry can exhibit unconventional spin-orbit fields, including fully momentum-aligned radial Rashba fields as seen in twisted van der Waals homobilayers. We theoretically study Cooper-pair transfer in superconductor/ferromagnet/superconductor Josephson junctions with crossed (tangential and radial) interfacial Rashba fields. We find that their interplay leads to what we call the unconventional supercurrent diode effect (SDE), where supercurrent rectification occurs even with collinear (with respect to the current) barrier magnetization, not possible for conventional spin-orbit fields. This SDE, distinct from conventional Rashba-induced effects on Cooper-pair momenta, arises from the spin precession in the magnetic barrier. We propose it as a sensitive probe of chiral spin textures.

cond-mat.supr-con↗

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

Upper Bound on Locally Extractable Energy from Entangled Pure State under Feedback Control

We introduce an effective thermodynamics for multipartite entangled pure states and derive an upper bound on extractable energy with feedback control from a subsystem under a local Hamiltonian. The inequality that gives the upper bound corresponds to the second law of information thermodynamics in our effective thermodynamics. In addition, we derive a more general bound that is determined only by an initial state and the local Hamiltonian. This bound gives an explicit relationship between the extractable energy and the entanglement structure of the initial state. We also investigate the tightness of the upper bounds and show that the bounds can be achieved in a simple example.

quant-ph↗

arXiv2023

Dynamics of an Exciton-phonon Triangle under Photoirradiation

Herein, the dynamics of excitons coupled with optical phonons in a triangular system is numerically studied. By representing the excitons by quasi-spin states, the similarity between the chiral spin states and the exciton chiral states is discussed. In particular, the optical control of excitons is discussed, where photoirradiation causes the switching of the exciton states on the ultrafast time scale by Raman scattering. A phase diagram is obtained based on the ground-state properties of the system determined by the magnitudes of the exciton-phonon interactions and exciton transfer energy. By varying the frequency and/or intensity of light, a transition between exciton-phonon composite states is induced, which suggests the possibility of the coherent control of the chiral properties of excitonic systems via phonon excitation.

cond-mat.mes-hall↗

arXiv2023

Quantum Energy Teleportation and Entropy Change due to Feedback Control in One-Dimensional Heisenberg Model

We study the quantum energy teleportation in a four-spin one-dimensional Heisenberg model. A local magnetic field is applied at the edge sites to control the degree of the ground-state entanglement. In the teleportation protocol, an energy sender performs a projective measurement at one edge site, while an energy receiver performs a feedback control at the other edge site dependent on the measurement result to extract energy. We find that the energy extracted by the receiver takes a maximum at intermediate value of the local magnetic field. We also find that this magnetic-field behavior is almost proportional to entropy changes due to the feedback control. The role of a feedback control in an entropy change is discussed in terms of entanglement thermodynamics.

quant-ph↗

arXiv2023

Quasi-Particle Dynamics in Quasi-Periodic Ising Model with Temporally Fluctuating Transverse Fields

We study quasi-particle dynamics in a quasi-periodic Ising model with temporally fluctuating transverse fields. Specifically, we calculate the dynamical exponents of the standard deviation of a quasi-particle spreading under a field chosen randomly from binary values $\pm h$ at every time interval. We find that the short-time behavior of the dynamical exponents depends on the interval of the temporally fluctuating fields. We also reveal how the quasi-particle dynamics affects the relaxation of spin-spin correlation functions. The dynamics can be explained via the overlap between the eigenvectors of a Hamiltonian with $\pm h$.

cond-mat.stat-mech↗

arXiv2023

Photoinduced pseudospin-wave emission from charge-density-wave domain wall with superconductivity

We study photoinduced dynamics triggered by an inhomogeneity due to competition between charge density waves (CDWs) and superconductivity. As a simple example, we consider the superconducting (SC) interface between two CDW domains with opposite signs. The real-time dynamics are calculated within the time-dependent Hartree--Fock--Bogoliubov framework, where the order parameter dynamics and the nonequilibrium quasiparticle distribution functions are studied. We also calculate the various dynamical response functions within a generalized random phase approximation. Through comparisons between the real time dynamics and the analysis of the response functions, it is found that the photo-driven SC interface can emit collective modes of the SC order parameter. This is analogous to the spin wave emission from the magnetic domain wall in an antiferromagnet, particularly in the case of a low driving frequency, where the order parameters can be mapped onto the pseudospin picture. In the high-frequency case, we find a domain wall melting caused by changes in the quasiparticle distribution, which induces superconductivity in the whole system.

cond-mat.supr-con↗