arXiv subjects

Shu Chen

Publications and source records attributed to Shu Chen.

At least 19 recordsLinked to original sources

arXiv2026

Bethe-root configurations and spectral degeneracy in the open XXZ chain with degenerate boundaries

We investigate the structure of Bethe-root configurations in the spin-1/2 XXZ chain with degenerate open boundaries. The physical solutions of the Bethe Ansatz equations are classified into three types in the fully degenerate case and two types in the partially degenerate case, for which we propose counting formulas for the number of physical solution sets of each type. Furthermore, we observe spectral degeneracies in the fully degenerate case and show that they can be naturally explained by the presence of specific phantom strings in the Bethe roots. The classification and resulting spectral degeneracies in the diagonal limit are also discussed.

math-ph↗

arXiv2026

Dynamical zero modes, boundary dependence, and numerical instability in dynamical quantum phase transitions

Boundary conditions are usually expected to cause only finite-size corrections to bulk quantities, but this expectation can fail for dynamical quantum phase transitions. In this work, we show that such boundary dependence is encoded in dynamical zero modes (DZMs) of the Loschmidt matrix, which are defined as singular vectors whose singular values vanish in the thermodynamic limit. Using the Su-Schrieffer-Heeger (SSH) and extended SSH models as examples, we find that the time interval where the Loschmidt rate functions (LRFs) under periodic and open boundary conditions differ coincides with the emergence of DZMs in the open-boundary Loschmidt matrix. These modes carry the boundary-dependent contribution: removing them from the open-boundary LRF recovers the periodic-boundary result. We further show that these DZMs lead to finite-precision numerical instability, since their finite-size singular values decay exponentially with system size and eventually become unresolved in fixed-precision arithmetic. A reliable small-size branch before this loss of precision can be used to estimate the thermodynamic LRF by linear extrapolation. Our results identify DZMs as both a diagnostic of boundary-dependent LRFs and the origin of the associated numerical instability.

quant-ph↗

arXiv2026

Soft-Dimuon Signature from Two-Component Scalar Dark Matter at the LHC

We explore the potential of the Large Hadron Collider to probe a two-component scalar dark matter scenario in the opposite-sign dimuon plus missing transverse energy final state, accompanied by a hard jet. The signal features a soft dimuon system with an invariant mass well below $m_Z$. We consider a 3-Higgs Doublet Model with one active and two inert scalar doublets, where a $Z_2 \times Z_2'$ symmetry stabilises the lightest neutral scalar in each inert sector, yielding two scalar DM candidates. The relevant parameter space is mapped in terms of the two DM masses and the mass splittings between each DM candidate and its corresponding next-to-lightest scalar state. We perform a detector-level Monte Carlo analysis and design a dedicated cut-based selection, including a transverse-mass requirement adapted to the signal topology. For a representative benchmark, we obtain $S/B\simeq 9.8%$ and a statistical-only significance of $S/\sqrt{B}=1.35$ at Run 3 with ${\cal L}=300~{\rm fb}^{-1}$, increasing to $S/\sqrt{B}=4.93$ under a statistical-only extrapolation to ${\cal L}=4~{\rm ab}^{-1}$. Before the full selection, the two dark sectors generate a double-bump structure in the dimuon invariant-mass distribution. After the cuts optimised for inclusive sensitivity, however, this feature is not statistically robust enough to establish the two-component origin of the signal. The benchmark is underabundant and is interpreted as a subdominant two-component DM scenario, while the collider analysis remains independent of its cosmological abundance. Although the numerical study is carried out in the I(2+1)HDM, the results are applicable to weakly interacting sectors with similar electroweak associated production and cascade decays, where a heavier state separated from the DM candidate by less than $m_Z$ produces a soft muon pair via an off-shell $Z$ boson.

hep-ph↗

arXiv2026

Open LHC Monte Carlo Event Generation

The LHC physics programme involves a vast amount of Monte Carlo event simulation. This paper reviews current efforts towards sharing the generated events as Open Data. Open Event Generation helps reduce duplication of effort and resource consumption, and benefits the whole High Energy Physics community. We give examples of use cases and user experiences, discuss financial and environmental savings, and suggest future directions.

hep-ph↗

arXiv2026

Critical Entanglement Dynamics at Dynamical Quantum Phase Transitions

We investigate the critical behavior of momentum-space entanglement entropy at dynamical quantum phase transitions (DQPTs) in translationally invariant two-band insulators and superconductors. By analyzing the Su-Schrieffer-Heeger model, the quantum XY chain, and the Haldane model, we establish that the geometric DQPT condition $\hat{\textbf{d}}_{\textbf{k}}^{i} \cdot \hat{\textbf{d}}_{\textbf{k}}^{f} = 0$ manifests as exact degeneracy $p_{\textbf{k}^{*}}=1/2$ in the entanglement spectrum defined with respect to the post-quench eigenbasis, yielding a maximal momentum-space entropy of $\ln 2$. In one dimension, critical momenta appear as isolated points, whereas in two dimensions they form continuous one-dimensional manifolds, reflecting the dimensional dependence of the underlying critical structure. Importantly, alternative bipartitions such as the sublattice basis produce qualitatively different behavior: the entropy becomes explicitly time-dependent and attains a minimum at DQPT critical times, underscoring the essential role of basis selection. Our results establish that momentum-space entanglement entropy, when evaluated in the appropriate eigenbasis, provides a robust, time-independent diagnostic of DQPTs and offers a unified geometric perspective linking entanglement, topology, and non-equilibrium criticality.

quant-ph↗

arXiv2026

VectraFlow: Long-Horizon Semantic Processing over Data and Event Streams with LLMs

Monitoring continuous data for meaningful signals increasingly demands long-horizon, stateful reasoning over unstructured streams. However, today's LLM frameworks remain stateless and one-shot, and traditional Complex Event Processing (CEP) systems, while capable of temporal pattern detection, assume structured, typed event streams that leave unstructured text out of reach. We demonstrate VectraFlow, a semantic streaming dataflow engine, to address both gaps. VectraFlow extends traditional relational operators with LLM-powered execution over free-text streams, offering a suite of continuous semantic operators -- filter, map, aggregate, join, group-by, and window -- each with configurable throughput-accuracy tradeoffs across LLM-based, embedding-based, and hybrid implementations. Building on this, a semantic event pattern operator lifts complex event processing to unstructured document streams, combining LLM-based event extraction with NFA-based temporal rule matching for stateful reasoning over sequences of semantic events. In this demonstration, users will interact with VectraFlow's live query interface to compose semantic pipelines over clinical document streams. Attendees will compile natural language intents into executable operator graphs, inspect intermediate stateful outputs, and observe end-to-end temporal pattern detection, from raw text to matched event cohorts.

cs.DB↗

arXiv2026

Distribution of fidelity zeros in two-band topological models

We investigate the distribution of fidelity zeros in two-band topological models by extending the phase transition driving parameter into the complex plane. Within the biorthogonal formulation, we unveil that fidelity zeros are related to momentum modes for which the real part of the energy gap vanishes. Guided by this relation, we analyze the Kitaev chain, the Haldane model, and the Qi-Wu-Zhang (QWZ) model. In finite-size systems the zeros form discrete lines parallel to the imaginary axis, while in the thermodynamic limit they accumulate into extended regions in the complex parameter plane. For the Kitaev and Haldane models, the accessible interval of the real part of the complexified parameter is bounded by the critical points of the corresponding topological transitions. For the QWZ model, the transitions at $u = \pm2$ are identified in the same way, whereas the critical point at $u = 0$ is signaled by fidelity zeros crossing the real axis. These results extend the fidelity-zero framework to topological quantum phase transitions and clarify how critical information is encoded in complexified parameter space.

quant-ph↗

arXiv2026

Topological Anderson insulator and reentrant topological transitions in a mosaic trimer lattice

We study the topological properties of a one-dimensional quasiperiodic-potential-modulated mosaic trimer lattice. To begin with, we first investigate the topological properties of the model in the clean limit free of quasiperiodic disorder based on analytical derivation and numerical calculations of the Zak phase $Z$ and the polarization $P$. Two nontrivial topological phases corresponding to the $1/3$ filling and $2/3$ filling, respectively, are revealed. Then we incorporate the mosaic modulation and investigate the influence of quasiperiodic disorder on the two existing topological phases. Interestingly, it turns out that quasiperiodic disorder gives rise to multiple distinct effects for different fillings. At $2/3$ filling, the topological phase is significantly enhanced by the quasiperiodic disorder and topological Anderson insulator emerges. Based on the calculations of polarization and energy gap, we explicitly present corresponding topological phase diagram in the $\lambda-J$ plane. While for the $1/3$ filling case, % the topological phase is dramatically suppressed by the same quasiperiodic disorder. the quasiperiodic disorder dramatically compresses the topological phase, and strikingly, further induces the emergence of reentrant topological phase transitions instead. Furthermore, we verify the topological phase diagrams by computing the many-body ground state fidelity susceptibility for both the $1/3$ filling and $2/3$ filling cases. Our work exemplifies the diverse roles of quasiperiodic disorder in the modulation of topological properties, and will further inspire more research on the competitive and cooperative interplay between topological properties and quasiperiodic disorder.

cond-mat.dis-nn↗

arXiv2026

Seeking Human Security Consensus: A Unified Value Scale for Generative AI Value Safety

The rapid development of generative AI has brought value- and ethics-related risks to the forefront, making value safety a critical concern while a unified consensus remains lacking. In this work, we propose an internationally inclusive and resilient unified value framework, the GenAI Value Safety Scale (GVS-Scale): Grounded in a lifecycle-oriented perspective, we develop a taxonomy of GenAI value safety risks and construct the GenAI Value Safety Incident Repository (GVSIR), and further derive the GVS-Scale through grounded theory and operationalize it via the GenAI Value Safety Benchmark (GVS-Bench). Experiments on mainstream text generation models reveal substantial variation in value safety performance across models and value categories, indicating uneven and fragmented value alignment in current systems. Our findings highlight the importance of establishing shared safety foundations through dialogue and advancing technical safety mechanisms beyond reactive constraints toward more flexible approaches. Data and evaluation guidelines are available at https://github.com/acl2026/GVS-Bench. This paper includes examples that may be offensive or harmful.

cs.CY↗

arXiv2026

Maximal Entanglement and Frozen Information: A Unified Framework for Dynamical Quantum Phase Transitions

Dynamical quantum phase transitions (DQPTs) are temporal singularities marked by zeros of the Loschmidt echo, yet their underlying quantum-information structure remains elusive. Here, we introduce a momentum-resolved entanglement entropy as a direct probe of DQPTs in translation-invariant free systems. We analytically establish that every critical momentum mode $k^{*}$ associated with a DQPT saturates its entanglement to the maximal value $\ln{2}$, coinciding with the vanishing of the Loschmidt echo. Crucially, we demonstrate that this maximal entanglement universally suppresses information scrambling: a momentum-resolved out-of-time-ordered correlator (OTOC) vanishes identically for all times at $k^{*}$. These three signatures -- Fisher zeros, maximal entanglement, and vanished OTOC -- are proved to be equivalent in both the transverse-field Ising and Su-Schrieffer-Heeger models, despite their distinct bipartitions (momentum-pair vs. sublattice). Our results establish a unified, information-theoretic framework for DQPTs, revealing them a points where quantum correlations saturate and information flow halts. This work elevates entanglement and scrambling to central dynamical order parameters, offering a universal perspective on nonequilibrium quantum critically.

quant-ph↗

arXiv2025

Emergence of long-range entanglement and odd-even effect in periodic generalized quantum cluster models

We investigate the entanglement properties in a generalized quantum cluster model under periodic boundary condition. By evaluating the quantum conditional mutual information entropy under four subsystem partitions, we identify clear signatures of long-range entanglement. Specifically, when both the system size $N$ and the interaction range $m$ are odd, the system exhibits nonzero four-part quantum conditional mutual information entropies in infinitesimal but finite field. This nonvanishing four-part quantum conditional mutual information entropy directly signals the presence of long-range entanglement. In contrast, all other combination of $N$ and $m$ yield vanishing four-part quantum conditional mutual information entropy. Remarkably, in the case of $N, m \in \text{odd}$, these long-range entangled features persist even in the presence of a large transverse field, demonstrating their robustness against quantum fluctuations. These results demonstrate how the interplay between system size and interaction range governs the emergence of long-range entanglement in one-dimensional generalized quantum cluster model.

quant-ph↗

arXiv2025

Tunable discrete quasi-time crystal from a single drive

The search for exotic temporal orders in quantum matter, such as discrete quasi-time crystals (DQTCs), has become an important theme in nonequilibrium physics. However, realizing these phases has so far required complex protocols, such as drives with multiple incommensurate frequencies. Here, we present a significantly simpler mechanism: the emergence of DQTCs in a dissipative collective spin system subjected to only a single periodic drive. Remarkably, the characteristic frequencies of this novel phase are not fixed but can be continuously tuned by varying the strength of the drive. Even more strikingly, this tunability is punctuated by Arnold tongues, within which the response main frequency locks to rational fractions of the drive. Our model further provides a unified framework that also encompasses stationary, discrete time crystals and chaotic phases. This discovery simplifies the requirements for generating complex temporal orders and opens a viable route towards the experimental control and manipulation of quasi-time crystalline matter.

quant-ph↗

arXiv2025

Multiple reentrant topological windows induced by generalized Bernoulli disorder

We investigate reentrant topological transitions in a one-dimensional Su-Schrieffer-Heeger chain with generalized Bernoulli disorder in the intradimer hopping amplitudes. Owing to its independently tunable values and probabilities, the multivalued disorder distribution provides a direct way to control the topological phase diagram. We show that increasing the disorder strength can split the nontrivial regime into multiple disconnected topological windows, whose number, widths, and locations are determined by the distribution parameters. The phase boundaries are derived analytically from the zero-mode inverse localization length and are governed by a weighted geometric mean of the disordered hopping amplitudes, in agreement with numerical results from the reflection-matrix topological quantum number and the real-space winding number. We also show that the mean chiral displacement dynamically identifies these reentrant windows. These results demonstrate how multivalued random disorder can organize and tune reentrant topological behavior in one-dimensional chiral lattices.

physics.optics↗

arXiv2025

Continuous Prompts: LLM-Augmented Pipeline Processing over Unstructured Streams

Monitoring unstructured streams increasingly requires persistent, semantics-aware computation, yet today's LLM frameworks remain stateless and one-shot, limiting their usefulness for long-running analytics. We introduce Continuous Prompts (CPs), the first framework that brings LLM reasoning into continuous stream processing. CPs extend RAG to streaming settings, define continuous semantic operators, and provide multiple implementations, primarily focusing on LLM-based approaches but also reporting one embedding-based variants. Furthermore, we study two LLM-centric optimizations, tuple batching and operator fusion, to significantly improve efficiency while managing accuracy loss. Because these optimizations inherently trade accuracy for speed, we present a dynamic optimization framework that uses lightweight shadow executions and cost-aware multi-objective Bayesian optimization (MOBO) to learn throughput-accuracy frontiers and adapt plans under probing budgets. We implement CPs in the VectraFlow stream processing system. Using operator-level microbenchmarks and streaming pipelines on real datasets, we show that VectraFlow can adapt to workload dynamics, navigate accuracy-efficiency trade-offs, and sustain persistent semantic queries over evolving unstructured streams.

cs.DB↗

arXiv2025

Mixed-State Berry Curvature in quantum multiparameter estimations

For pure states, the quantum Berry curvature was well studied. However, the quantum curvature for mixed states has received less attention. From the concept of symmetric logarithmic derivative, we introduce a mixed-state quantum curvature and find that it plays a key role in the field of multi-parameter precision estimations. Through spectral decomposition, we derive the mixed-state Berry curvature for both the full-rank and non-full-rank density matrices. As an example, we obtain the exact expression of the Berry curvature for an arbitrary qubit state.

quant-ph↗

arXiv2025

Entanglement manifestation of knot topology in a non-Hermitian lattice

Although the homotopy-knot theory has been utilized to implement effective topological classification for non-Hermitian systems, the physical implications underlying distinct knot topologies remain ambiguous and are rarely addressed. In this work, we propose a one-dimensional non-Hermitian four-band lattice model and map out its phase diagram according to the distinct knot structures residing in the moment space. The topological phase diagram is ascertained through a spectral winding number. Furthermore, we derive the exact analytic formula for the phase boundaries that delineate different knot topologies. To explore the concrete physical implications of distinct knot topologies, we investigate the many-body ground state entanglement entropy for free fermions loaded on such non-Hermitian lattice in real space. It turns out that different knot topologies imply different magnitudes of entanglement. Moreover, we show that the central charge c extracted from systematic finite-size scaling of entanglement entropy provides effective description of the phase diagram of the knot topology. Finally, we further confirm the phase boundaries for the topological phase transitions alternatively by numerical calculations of the many-body ground state fidelity susceptibility. Our results showcase the connection between knot topology and entanglement of non-Hermitian systems and may facilitate further exploration of the profound and practical physical implications of knot topology.

quant-ph↗

arXiv2025

Making Prompts First-Class Citizens for Adaptive LLM Pipelines

Modern LLM pipelines increasingly resemble complex data-centric applications: they retrieve data, correct errors, call external tools, and coordinate interactions between agents. Yet, the central element controlling this entire process -- the prompt -- remains a brittle, opaque string that is entirely disconnected from the surrounding program logic. This disconnect fundamentally limits opportunities for reuse, optimization, and runtime adaptivity. In this paper, we describe our vision and an initial design of SPEAR (Structured Prompt Execution and Adaptive Refinement), a new approach to prompt management that treats prompts as first-class citizens in the execution model. Specifically, SPEAR enables: (1) structured prompt management, with prompts organized into versioned views to support introspection and reasoning about provenance; (2) adaptive prompt refinement, whereby prompts can evolve dynamically during execution based on runtime feedback; and (3) policy-driven control, a mechanism for the specification of automatic prompt refinement logic as when-then rules. By tackling the problem of runtime prompt refinement, SPEAR plays a complementary role in the vast ecosystem of existing prompt optimization frameworks and semantic query processing engines. We describe a number of related optimization opportunities unlocked by the SPEAR model, and our preliminary results demonstrate the strong potential of this approach.

cs.DB↗

arXiv2025

Hierarchy of localized many-body bound states in an interacting open lattice

We unveil the mechanism for the formation of puzzled boundary-localized bound states in a spinless fermionic open lattice with nearest-neighbor interactions. By solving the Bethe-ansatz equation analytically, we uncover asymmetrical string solutions corresponding to the boundary-localized bound states, which emerge in systems with at least three particles. The localized bound states can become bound states in continuum in a suitable parameter region. When the number of particles increases to five or more, additional bound states away from the edge are also observed. Through rigorous analysis, we derive recurrence relations of the quasi-momentum of the localized states as a function of the number of particles, predicting the presence of hierarchy of localized many-body bound states in interacting open lattices.

cond-mat.quant-gas↗