arXiv subjects

Chi-Ting Liu

Publications and source records attributed to Chi-Ting Liu.

3 recordsLinked to original sources

arXiv2026

Even-harmonic generation from topological edge states in generalized Su-Schrieffer-Heeger models

High-order harmonic generation (HHG) in solids has emerged as a powerful probe of symmetry and topological properties in quantum materials. In this work, we investigate the HHG response in one-dimensional solids with edge or midgap states under global and local illumination. We numerically compute the HHG spectrum for the Su-Schrieffer-Heeger (SSH) model with next-nearest-opposite sublattice hopping, dubbed the extended SSH (ESSH) model, and the Rice-Mele model, a one-dimensional system with broken inversion symmetry introduced via staggered on-site potentials. By contrasting the spectral features of the ESSH and Rice-Mele models under global illumination, our analysis reveals that although midgap states provide additional pathways for transitions, the resulting interference is destructive, leading to spectral features distinct from those of edge states. Furthermore, when a single boundary of the topological insulator is locally illuminated, the HHG spectrum of the edge states exhibits vanishing odd harmonics, leaving even harmonics dominant in the spectrum. We identify this even-harmonic selection rule as a consequence of the zero-energy character of the edge states and the particle-hole symmetry of the system, which enforces even field parity of the zero-mode response. These findings reveal that the spatial location of the laser illumination offers a route to control the symmetry of the system, thereby selectively suppressing or enhancing even- and odd-order harmonics in low-dimensional nanostructures.

cond-mat.mes-hall↗

arXiv2025

CAPM: Fast and Robust Verification on Maxpool-based CNN via Dual Network

This study uses CAPM (Convex Adversarial Polytope for Maxpool-based CNN) to improve the verified bound for general purpose maxpool-based convolutional neural networks (CNNs) under bounded norm adversarial perturbations. The maxpool function is decomposed as a series of ReLU functions to extend the convex relaxation technique to maxpool functions, by which the verified bound can be efficiently computed through a dual network. The experimental results demonstrate that this technique allows the state-of-the-art verification precision for maxpool-based CNNs and involves a much lower computational cost than current verification methods, such as DeepZ, DeepPoly and PRIMA. This method is also applicable to large-scale CNNs, which previous studies show to be often computationally prohibitively expensive. Under certain circumstances, CAPM is 40-times, 20-times or twice as fast and give a significantly higher verification bound (CAPM 98% vs. PRIMA 76%/DeepPoly 73%/DeepZ 8%) as compared to PRIMA/DeepPoly/DeepZ. Furthermore, we additionally present the time complexity of our algorithm as $O(W^2NK)$, where $W$ is the maximum width of the neural network, $N$ is the number of neurons, and $K$ is the size of the maxpool layer's kernel.

cs.CV↗

arXiv2023

A Brief Survey of Open Radio Access Network (O-RAN) Security

Open Radio Access Network (O-RAN), a novel architecture that separates the traditional radio access network (RAN) into multiple disaggregated components, leads a revolution in the telecommunication ecosystems. Compared to the traditional RAN, the proposed O-RAN paradigm is more flexible and more cost-effective for the operators, vendors, and the public. The key design considerations of O-RAN include virtualization and intelligent capabilities in order to meet the new requirements of 5G. However, because of the open nature and the newly imported techniques in O-RAN architecture, the assessment of the security in O-RAN architecture during its early development stage is crucial. This project aims to present an investigation of the current ORAN architecture from several attack surfaces, including (1) Architectural openness, (2) Cloud and Virtualization, (3) Network slicing, and (4) Machine Learning. The existing attack surfaces and corresponding mitigation methods of these attacks are also surveyed and provided in this report, serving as a guiding principle and valuable recommendation for the O-RAN implementers and framework designers.

cs.NI↗