arXiv subjects

Yibo Liang

Publications and source records attributed to Yibo Liang.

4 recordsLinked to original sources

arXiv2026

An Electromagnetic Particle-Particle Method for Relativistic Electron Bunch Dynamics from Early Expansion to Long-Range Transport

Particle-mesh methods, such as the particle-in-cell (PIC) method, cannot retain exact pairwise interaction at sub-cell scales. For dense nonneutral relativistic electron bunches, this makes it difficult to accurately capture the inter-particle electromagnetic interaction and the associated bunch divergence. In this work, the previously developed electromagnetic particle-particle (EM-PP) model for relativistic two-particle interaction is extended to many-particle electron bunch transport in the Earth's magnetosphere. The method combines the Li\'enard--Wiechert fields, an improved retarded-time evaluation procedure, and a relativistic particle pusher, and adopts a two-stage strategy to couple the dense early self-field-dominated evolution to the later long-range geomagnetic-field-controlled transport. The method provides a practical mesh-free approach for accurately simulating long-range transport of relativistic electron bunches when short-range electromagnetic interaction is important.

physics.plasm-ph↗

arXiv2026

When Safe Concepts Become Unsafe: Multi-Concept Compositional Vulnerabilities in Text-to-Image Models

Text-to-image (T2I) models are increasingly optimized for following user instructions faithfully. However, we find that this capability introduces a safety vulnerability we call Multi-Concept Compositional Unsafety (MCCU). MCCU occurs when multiple individually safe concepts, if combined in a single generation request, lead to harmful or sensitive visual outputs. Unlike prior jailbreak settings, MCCU does not rely on adversarial prompts, model access, or explicitly disallowed content. Instead, the risk emerges from how the model composes multiple safe visual concepts into a single scene. To systematically measure this threat, we build TwoHamsters, a large-scale evaluation framework consisting of 20k prompts, 51 curated concept pairs, and six risk categories. We evaluate 13 T2I models under a black-box setting. Our results show a clear conflict between instruction-following and safety: models that follow prompts more faithfully tend to produce more MCCU failures. For example, FLUX.1 achieves a 99.35% Unsafe Alignment Rate while only reaching a 1.57% MCCU Defense Rate. We further evaluate three representative defenses, including safety filtering, MCCU-specific detector fine-tuning, and concept erasure, all of which fail against unseen concept combinations. Our findings suggest that compositional reasoning in T2I models creates an attack surface that is not captured by existing safety mechanisms. We anticipate the release of TwoHamsters will catalyze community development of advanced generative defense mechanisms.

cs.CR↗

arXiv2025

Scalable and modular generation of multipartite entangled states through memory-enhanced fusion

Efficient generation of large-scale multipartite entangled states is a critical but challenging task in quantum information processing. Although generation of multipartite entanglement within a small set of individual qubits has been demonstrated, further scale-up in system size requires the connection of smaller entangled states into a larger state in a scalable and modular manner. Here we achieve this goal by implementing memory-enhanced fusion of two multipartite entangled states via photonic interconnects. Through asynchronous preparation of two tripartite W-state entanglements in two spatially-separated modules of atomic quantum memories and on-demand fusion via single-photon interference, we demonstrate the creation of a four-partite W-state entanglement shared by two remote quantum memory modules in a heralded way. We further transfer the W state from the memory qubits to the photonic qubits, and confirm the genuine four-partite entanglement through witness measurements. We then demonstrate memory-enhanced scaling in efficiencies in the entanglement fusion. The demonstrated scalable generation and fusion of multipartite entangled states pave the way towards realization of large-scale distributed quantum information processing in the future.

quant-ph↗

arXiv2024

Fast delivery of heralded atom-photon quantum correlation over 12km fiber through multiplexing enhancement

Distributing quantum entanglement between distant parties is a significant but difficult task in quantum information science, as it can enable numerous applications but suffers from exponential decay in the quantum channel. Quantum repeater is one of the most promising approaches towards this goal. In a quantum repeater protocol, it is essential that the entanglement generation speed within each elementary link is faster than the memory decoherence rate, to enable the scale-up of the quantum repeater by connecting neighboring repeater segments. This stringent requirement has not been implemented over a fiber of metropolitan scale so far. As a step towards this challenging goal, in this work we experimentally realize multiplexing-enhanced generation of heralded atom-photon quantum correlation over a 12km fiber. We excite the memory modes in a multiplexed quantum memory successively to generate 280 pairs of atom-photon quantum correlations with a train of photonic time-bin pulses filling the long fiber. After successful detection of a heralding signal, the excited memory mode can be identified and retrieved into idler photons on demand with either fixed or variable storage time. With the multiplexing enhancement, the heralding rate of atom-photon correlation can reach 1.95kHz, and the ratio between the quantum correlation generation rate to memory decoherence rate can be improved to 0.46 for a fiber length of 12km, which is so far the best for long fiber length (>10km) to our knowledge. This work therefore constitutes an important step towards the realization of a large-scale quantum repeater network.

quant-ph↗