arXiv subjects

Zhenjiang Zhao

Publications and source records attributed to Zhenjiang Zhao.

3 recordsLinked to original sources

arXiv2026

Orthogonal Attosecond Control of Solid-State Harmonics by Optical Waveforms and Quantum Geometry Engineering

High-harmonic generation (HHG) in two-dimensional materials offers a compelling route toward compact extreme ultraviolet sources and probing electron dynamics on the attosecond scale. However, achieving precise control over the emission and disentangling the complex interplay between intraband and interband quantum pathways remains a central challenge. Here, we demonstrate through first-principles simulations that HHG in monolayer WS2 can be subjected to precise, complementary control by combining all-optical two-color laser fields with mechanical strain engineering. This dual-mode strategy provides distinct, orthogonal control over harmonic yield, polarization, and spectral features. We reveal that sculpting the two-color field's relative phase provides a sub-femtosecond switch for the quantum coherence of electron-hole pairs, thereby optimizing harmonic emission. Crucially, we uncover that tensile strain modulates the total harmonic yield and specifically amplifies the perpendicular harmonic component by nearly a factor of two. This enhancement arises through a dual mechanism - while strain-modified band dispersion enhances the intraband current, a significant reshaping of the Berry curvature (BC) substantially increases the anomalous velocity contribution to the interband response. This quantum geometric effect manifests as a robust, monotonic dependence of the harmonic yield on strain and a significant amplification of the perpendicularly polarized harmonics, providing a clear experimental signature for probing quantum geometric effects. Our findings establish a versatile framework for optimizing solid-state HHG and introduce a powerful all-optical method to map strain and quantum geometric properties of materials, positioning monolayer WS2 as a model system for exploring attosecond physics at the nexus of bulk and atomic scales.

physics.comp-ph↗

arXiv2025

Quantitative Verification of Fairness in Tree Ensembles

This work focuses on quantitative verification of fairness in tree ensembles. Unlike traditional verification approaches that merely return a single counterexample when the fairness is violated, quantitative verification estimates the ratio of all counterexamples and characterizes the regions where they occur, which is important information for diagnosing and mitigating bias. To date, quantitative verification has been explored almost exclusively for deep neural networks (DNNs). Representative methods, such as DeepGemini and FairQuant, all build on the core idea of Counterexample-Guided Abstraction Refinement, a generic framework that could be adapted to other model classes. We extended the framework into a model-agnostic form, but discovered two limitations: (i) it can provide only lower bounds, and (ii) its performance scales poorly. Exploiting the discrete structure of tree ensembles, our work proposes an efficient quantification technique that delivers any-time upper and lower bounds. Experiments on five widely used datasets demonstrate its effectiveness and efficiency. When applied to fairness testing, our quantification method significantly outperforms state-of-the-art testing techniques.

cs.LG↗

arXiv2025

First-principles design of stable spin qubits in monolayer MoS$_2$ with elemental defect engineering

Quantum information science (QIS), encompassing technologies such as quantum computing, sensing, and communication, relies on the development and manipulation of quantum bits (qubits). Recently, two-dimensional (2D) materials -- characterized by their atomic thinness and external controllability -- have emerged as promising candidates for qubit fabrication and manipulation at room temperature. In this study, we propose that antisite defects (MX) in 2D transition metal disulfides (TMDs) can serve as tunable quantum defects with controlled positioning. Using first-principles atomic structure simulations, we identify six thermodynamically stable neutral antisite defects (MX, where M = Mg, Ca, Sr, Ba, Zn, Cd; X = S) in monolayer 1H-MoS$_2$. These defects exhibit potential as spin-defected qubits with stable triplet ground states. Additionally, we demonstrate that the reduction of the bandgap leads to significant fluctuations in the absorption coefficient within the low-energy range, resulting in the optical response within the desired telecommunication band, which is advantageous for quantum communication applications. The zero-phonon line (ZPL) associated with these qubits can serve as an effective identifier. This work presents the novel, tunable approach to exploiting defects in 2D materials, opening new possibilities for the development of qubit platforms in quantum information technology.

physics.app-ph↗