arXiv subjects

Naoki Negishi

Publications and source records attributed to Naoki Negishi.

4 recordsLinked to original sources

arXiv2026

Spatial-Order Hierarchy of Time-Dependent Exchange-Correlation Potential

Exact time-dependent density-functional theory separates the exchange-correlation potential into interaction and kinetic-correlation components, but the structural relation between them remains unknown. We establish a representability constraint based on the off-diagonal expansion of the one-electron reduced density matrix relative to a time-dependent Hartree-Fock (TDHF) reference. A non-zero linear term generates a non-HF current density while the kinetic-correlation component remains HF representable; higher-order off-diagonal structure activates the kinetic component. In a one-dimensional two-electron correlation quench, retaining the exact interaction component while setting the kinetic component to zero suppresses the density broadening of the exact evolution. These results establish a hierarchy of density equations of motion and provide an exact constraint for non-adiabatic functional construction.

quant-ph↗

arXiv2026

Beyond Commutativity: Redesigning Trotter Decomposition via Local Symmetry

The product formula, commonly known as Trotter decomposition, is a central tool for digital quantum simulation, whose performance depends critically on how the Hamiltonian is partitioned into tractable blocks. Standard decompositions typically rely on direct commutativity among Hamiltonian terms in a chosen operator representation, which can lead to large residual errors and deep circuits for complex, practically relevant many-body quantum systems. We address this fundamental bottleneck by introducing a new decomposition principle that goes beyond commutativity, grouping Hamiltonian terms into local three-site clusters according to the underlying SU(2) symmetry of the local dynamics. We show that three-site generators fall into at most four SU(2)-symmetry classes, each admitting an effective two-qubit SU(4) representation with exact and efficient implementations. By reducing the number of clusters, this decomposition principle substantially suppresses commutator-induced errors and circuit overhead while preserving underlying physical structures that commutativity-based decompositions may violate. We demonstrate the proposed method on several physically relevant spin-lattice models, where the reduced cluster structure can even realise the second-order product formula without doubling the circuit depth, as would be required by conventional decompositions. Numerical simulations of a Kagome Heisenberg model with triangular spin-chirality interactions show that the proposed method reduces both state infidelity and average spin-chirality bias by more than three orders of magnitude compared with conventional decompositions, while using substantially fewer gates. These results establish local symmetry as a flexible and practical design principle for product-formula simulation, opening a route to more accurate and hardware-efficient simulations of broader classes of many-body systems.

quant-ph↗

arXiv2025

Quantum simulation of many-body dynamics with noise-robust Trotter decomposition based on symmetric structures

The Suzuki-Trotter decomposition, which digitalizes quantum time evolution, provides a promising framework for simulating quantum dynamics on quantum hardware and exploring quantum advantage over classical computation. However, conventional Trotter circuits require a large number of non-local gates, lowering their faithfulness to the ideal dynamics when implemented on current noisy quantum hardware. While most previous studies have focused on circuit optimization, we instead propose a new Trotter decomposition that is intrinsically circuit-efficient for simulating quantum dynamics on near-term devices. Our method substantially reduces both the residual error by Trotter decomposition and the number of CNOT operations compared to conventional Trotter decompositions by exploiting the symmetry of the target model to construct an effective Hamiltonian with fewer two-qubit gates. We demonstrate the noise robustness of the proposed approach through numerical simulations of a nine-site Heisenberg model under realistic noise, and further validate its experimental practicality on the IBM superconducting device, achieving a state fidelity exceeding $0.98$ when combined with quantum error mitigation in the three-site case. The proposed circuit design is also compatible with existing circuit optimization techniques. Our results establish a practical route toward noise-resilient quantum simulation in many-body dynamics.

quant-ph↗

arXiv2024

Theory of Frequency Fluctuation of Intramolecular Vibration in Solution Phase: Application to C--N Stretching Mode of Organic Compounds

We formulate frequency fluctuations of intramolecular vibrations of a solute by exploring the fluctuation of the electrostatic potential by solvents. We present a numerical methodology for estimating the frequency fluctuations; the methodology is based on the reference interaction site model self-consistent field with constrained spatial electron density distribution, a the theoretical model of solvation fields based on classical statistic mechanics. By applying the present theory to the C--N stretching vibrations of several nitrile compounds, our estimated frequency fluctuation scale and bandwidth shift by changing solvent kinds reproduced the experimental data. Further, we regard the standard deviation of the electrostatic potential as the multiple random variables for analyzing the frequency fluctuations. Our results reveal that the dominant fluctuation of the electrostatic field is almost parallel to the vibrational axis. Additionally, the fluctuations of electrostatic potential become spatially nonuniform as the solvents form stronger hydrogen bonds with the solute. The development of the solvation field confirms that the nonuniformity of the electrostatic field is crucial to the frequency fluctuation.

physics.chem-ph↗