arXiv subjects

Weiyu Wang

Publications and source records attributed to Weiyu Wang.

7 recordsLinked to original sources

arXiv2026

Ultralow Frequency Magnetic Comb Using Pulse Modulated Spin Maser

Frequency combs are widely used in fundamental physics and practical applications at various areas. Here we report the realization of an ultralow frequency magnetic comb using a pulse modulated spin maser in the Rb-Xe hybrid gaseous spin system. The magnetic frequency comb has a spectral distribution depending mainly on the pulse duration, the strength and phase shift of the feedback field. A simple theoretical model is given in terms of the spin echo chain and agrees well with the experimental results. The magnetic frequency comb works in an ultralow frequency range and reaches a frequency resolution down to tens of nanohertz.

physics.atom-ph↗

arXiv2026

Nonlinear dynamics in an artificial feedback spin maser II: dependence on feedback configurations and time crystal effects

Artificial feedback spin masers exhibit rich nonlinear dynamics, yet a systematic framework for understanding and controlling their behaviors remains elusive. In this paper, we consider the polarity and geometric configuration of the feedback field as important control parameters for studying the nonlinear dynamics of spin masers. By cooperatively tuning the strength and phase delay of feedback field, we investigate the spin dynamics at various configurations of the feedback field. Periodic, quasiperiodic and chaotic spin oscillations are uncovered. Specifically, a unique spin oscillation mode akin to the time crystal effects emerges within a certain parameter regime. This work presents a different viewpoint understanding the nonlinear dynamics of spin masers including the time crystal.

physics.atom-ph↗

arXiv2025

Prompt-in-Content Attacks: Exploiting Uploaded Inputs to Hijack LLM Behavior

Large Language Models (LLMs) are widely deployed in applications that accept user-submitted content, such as uploaded documents or pasted text, for tasks like summarization and question answering. In this paper, we identify a new class of attacks, prompt in content injection, where adversarial instructions are embedded in seemingly benign inputs. When processed by the LLM, these hidden prompts can manipulate outputs without user awareness or system compromise, leading to biased summaries, fabricated claims, or misleading suggestions. We demonstrate the feasibility of such attacks across popular platforms, analyze their root causes including prompt concatenation and insufficient input isolation, and discuss mitigation strategies. Our findings reveal a subtle yet practical threat in real-world LLM workflows.

cs.CR↗

arXiv2025

Observation of Time Crystal in a Spin Maser System

Pair interaction potentials between atoms in a crystal are in general non-monotonic in distance, with a local minimum whose position gives the lattice constant of the crystal. A temporal analogue of this idea of crystal formation is still pending despite intensive studies on the time crystal phase. In a hybrid spin maser system with a time delay feedback, we report the observation of a time crystal induced by a retarded interaction with a characteristic time scale. This nonequilibrium phase features a self-sustained oscillation with an emergent frequency other than the intrinsic Larmor precession frequency of the spin maser system. It is shown that the amplitude of the oscillation is robust against perturbation, while its time phase randomly distributes from 0 to $2π$ for different realizations, a signature of spontaneous time translation symmetry breaking. This time crystal phase emerges only when the feedback strength exceeds a critical value, at which the system experiences a first order phase transition. Such a retarded interaction induced time crystal is closer to the idea of crystal, compared to other time crystal realizations.

physics.atom-ph↗

arXiv2025

Laser power stabilization using conservation law in acoustic optic modulator

Laser power stabilization plays an important role in modern precision instruments based on atom-laser interactions. Here we demonstrate an alternative active control method of laser power utilizing the conservation law in an acoustic optic modulator (AOM). By adjusting the 1st order beam power to dynamically follow the fluctuation of the total power of all diffraction beams, the 0th order application beam as the difference term, is stabilized. Experimental result demonstrates that the relative power noise of the controlled application beam is reduced by a factor of 200, reaching $4 \times 10^{-6} $ Hz$^{-1/2}$ at 10$^{-4}$ Hz compared with the uncontrolled total power. Allan deviation shows that the application beam reaches a relative power instability of 3.28$\times 10^{-6}$ at 500 s averaging time. In addition, the method allows a high availability of total power source. The method opens a new way of laser power stabilization and shall be very useful in applications such as atomic clocks, laser interferometers and gyroscopes.

physics.optics↗

arXiv2018

Scaling Behavior of Anisotropy Relaxation in Deformed Polymers

Drawing an analogy to the paradigm of quasi-elastic neutron scattering, we present a general approach for quantitatively investigating the spatiotemporal dependence of structural anisotropy relaxation in deformed polymers by using small-angle neutron scattering. Experiments and non-equilibrium molecular dynamics simulations on polymer melts over a wide range of molecular weights reveal that their conformational relaxation at relatively high momentum transfer $Q$ and short time can be described by a simple scaling law, with the relaxation rate proportional to $Q$. This peculiar scaling behavior, which cannot be derived from the classical Rouse and tube models, is indicative of a surprisingly weak direct influence of entanglement on the microscopic mechanism of single-chain anisotropy relaxation.

cond-mat.soft↗

arXiv2017

Fingerprinting molecular relaxation in deformed polymers

The flow and deformation of macromolecules is ubiquitous in nature and industry, and an understanding of this phenomenon at both macroscopic and microscopic length scales is of fundamental and practical importance. Here we present the formulation of a general mathematical framework, which could be used to extract, from scattering experiments, the molecular relaxation of deformed polymers. By combining and modestly extending several key conceptual ingredients in the literature, we show how the anisotropic single-chain structure factor can be decomposed by spherical harmonics and experimentally reconstructed from its cross sections on the scattering planes. The resulting wavenumber-dependent expansion coefficients constitute a characteristic fingerprint of the macromolecular deformation, permitting detailed examinations of polymer dynamics at the microscopic level. We apply this approach to survey a long-standing problem in polymer physics regarding the molecular relaxation in entangled polymers after a large step deformation. The classical tube theory of Doi and Edwards predicts a fast chain retraction process immediately after the deformation, followed by a slow orientation relaxation through the reptation mechanism. This chain retraction hypothesis, which is the keystone of the tube theory for macromolecular flow and deformation, was critically examined by analyzing the fine features of the two-dimensional anisotropic spectra from small-angle neutron scattering by entangled polystyrenes. It is shown that the unique scattering patterns associated with the chain retraction mechanism were not experimentally observed. This result calls for a fundamental revision of the current theoretical picture for nonlinear rheological behavior of entangled polymeric liquids.

cond-mat.soft↗