arXiv subjects

Takuro Tanaka

Publications and source records attributed to Takuro Tanaka.

6 recordsLinked to original sources

arXiv2026

Robust Wavelength Selection for Partial Least Squares Sugar Content Estimation Using Combinatorial Bayesian Optimization

Wavelength selection is one of the important preprocessing methods in near-infrared spectroscopy to improve prediction accuracy and interpretability of spectral data. We formulate wavelength-region selection for sugar content estimation as a binary black-box optimization problem and propose a method based on Bayesian optimization. The proposed method constructs a sparse quadratic surrogate model and sequentially extracts interested wavelength regions by Thompson sampling. Minimizing an acquisition function is performed as a quadratic unconstrained binary optimization problem by simulated or quantum annealing. Experiments show that the proposed method improves the prediction accuracy of partial least squares regression and yields more consistent wavelength regions than genetic-algorithm-based selection and simulated annealing. Under one-bit local perturbations, the selected wavelength regions show minimal fluctuations in root mean square errors between observed and predicted values of a validation set. This local stability suggests that our method converges to a smoother error landscape and avoids isolated overfitted solutions. These results indicate that combinatorial Bayesian optimization is a useful framework for robust feature selection in spectroscopic prediction tasks.

stat.ML↗

arXiv2023

Exploration of new chemical materials using black-box optimization with the D-wave quantum annealer

In materials informatics, searching for chemical materials with desired properties is challenging due to the vastness of the chemical space. Moreover, the high cost of evaluating properties necessitates a search with a few clues. In practice, there is also a demand for proposing compositions that are easily synthesizable. In the real world, such as in the exploration of chemical materials, it is common to encounter problems targeting black-box objective functions where formalizing the objective function in explicit form is challenging, and the evaluation cost is high. In recent research, a Bayesian optimization method has been proposed to formulate the quadratic unconstrained binary optimization (QUBO) problem as a surrogate model for black-box objective functions with discrete variables. Regarding this method, studies have been conducted using the D-Wave quantum annealer to optimize the acquisition function, which is based on the surrogate model and determines the next exploration point for the black-box objective function. In this paper, we address optimizing a black-box objective function containing discrete variables in the context of actual chemical material exploration. In this optimization problem, we demonstrate results obtaining parameters of the acquisition function by sampling from a probability distribution with variance can explore the solution space more extensively than in the case of no variance. As a result, we found combinations of substituents in compositions with the desired properties, which could only be discovered when we set an appropriate variance.

quant-ph↗

arXiv2023

Virtual Screening of Chemical Space based on Quantum Annealing

For searching a new chemical material which satisfies the target characteristic value, for example emission wavelength, many cut and trial of experiments/calculations are required since the chemical space is astronomically large (organic molecules generates >10^60 candidates). Extracting feature importance is a method to reduce the chemical space, and limiting the search space to those features leads to shorter development time. Quantum computer can generate sampling data faster than classical computers, and this property is utilized to extract feature importance. In this paper, quantum annealer was used as a sampler to make data for extracting feature importance of material properties. By screening the chemical space with feature importance, it was found that the chemical space can be reduced to less than 1 percent. This result suggests that the acceleration of material research can be achievable.

quant-ph↗

arXiv2012

Extrinsic Spin Hall Effect Due to Transition-Metal Impurities

We investigate the extrinsic spin Hall effect in the electron gas model due to transition-metal impurities based on the single-impurity Anderson model with orbital degrees of freedom. Both the skew scattering and side jump mechanisms are analyzed in a unified way, and the significant role of orbital degrees of freedom are clarified. The obtained spin Hall conductivities are in proportion to the spin-orbit polarization at the Fermi level ($R = $) as is the case with the intrinsic spin Hall effect: skew scattering term $σ^{ss} ~ R δ_1/ρ$, and side jump term $σ^{sj} ~ R$, where $δ_1$ is the phase shift for $p$ ($l=1$) partial wave. Furthermore, the present study indicates the existence of a nontrivial close relationship between the intrinsic term $σ^{int}$ and the extrinsic side jump term $σ^{sj}$.

cond-mat.str-el↗

arXiv2010

Intrinsic Spin and Orbital Hall Effects in Heavy Fermion Systems

We study the intrinsic spin Hall effect (SHE) based on the orbitally degenerate periodic Anderson model, which is an effective model for heavy fermion systems. In the very low resistivity regime, the magnitude of the intrinsic spin Hall conductivity (SHC) is estimated as $2000 \sim 3000 \hbar e^{-1} Ω^{-1} cm^{-1}$; It is about 10 times larger than that in Pt. Its sign is negative (positive) in Ce (Yb) compound systems with $f^1$ ($f^{13}$) configuration. Interestingly, the obtained expression for the SHC depends only on the density of conduction electrons, but is independent of the strength of the c-f mixing potential and the mass-enhancement factor. The origin of the huge SHE is the spin-dependent Berry phase induced by the complex f-orbital wavefunction, which we call the "orbital Aharonov-Bohm effect".

cond-mat.str-el↗

arXiv2008

Theory of AC Anomalous Hall Conductivity in d-electron systems

To elucidate the intrinsic nature of anomalous Hall effect (AHE) in $d$-electron systems, we study the AC anomalous Hall conductivity (AHC) in a tight-binding model with ($d_{xz},d_{yz}$)-orbitals. We drive a general expression for the AC AHC $σ_{xy}(ω)$, which is valid for finite quasiparticle damping rate $γ$=$\hbar/2τ$, and find that the AC AHC is strongly dependent on $γ$. When $γ=+0$, the AC AHC shows a spiky peak at finite energy $Δ$ that originates from the interband particle-hole excitation, where $Δ$ represents the minimum band-splitting measured from the Fermi level. In contrast, we find that this spiky peak is quickly suppressed when $γ$ is finite. By using a realistic value of $γ(ω)$ at $ω=Δ/2$ in $d$-electron systems, the spiky peak is considerably suppressed. In the present model, the obtained results also represents the AC spin Hall conductivity in a paramagnetic state.

cond-mat.str-el↗