arXiv subjects

Yun-Jiang Wang

Publications and source records attributed to Yun-Jiang Wang.

At least 19 recordsLinked to original sources

arXiv2026

String Model Predicts Relaxation in Sheared Glass-Forming Liquids

Understanding how structural relaxation evolves from equilibrium to nonequilibrium conditions remains a central problem in glass physics. Using simulations of model glass formers under steady shear, we show that the String Model, which links stringlike cooperative rearrangements to relaxation in equilibrium glass-forming liquids, predicts the structural relaxation time across the full range of temperatures and shear rates investigated without additional nonequilibrium fitting parameters, when combined with a shear-dependent effective temperature that is captured by a generalized fluctuation-dissipation relation. These results indicate that equilibrium and nonequilibrium relaxation are governed by the same underlying cooperative mechanism, but they occur under different effective thermodynamic conditions under steady shear. More broadly, our study provides a unified microscopic description of thermal and mechanically driven dynamics in glass-forming liquids.

cond-mat.soft↗

arXiv2026

LEAD: A Local Ensemble-Assisted Parallel Decoding Framework for Quantum Tanner Codes

Quantum Tanner codes are a recently developed family of quantum error-correcting codes characterized by favorable asymptotic performance characteristics. Despite their theoretical potential, practical decoding algorithms that effectively leverage their structural properties remain limited. This work introduces LEAD (Local Ensemble-Assisted Decoder), a structure-aware decoding framework tailored for quantum Tanner codes. The proposed scheme leverages the decomposable structure of Cayley complexes to project the global code onto overlapping local subcodes defined by vertex neighborhoods, where error probabilities are estimated in parallel. To ensure global consistency, LEAD utilizes the inherent topological symmetry of the complex and introduces a soft-information regularization mechanism to mitigate local overconfidence during information aggregation. This framework enables highly parallelized, low-complexity decoding that is intrinsically compatible with various local search heuristics. Simulation results demonstrate that LEAD achieves significantly lower logical error rates than standard decoding framework while substantially reducing the average decoding latency and iteration count.

quant-ph↗

arXiv2026

Spectral Decomposition of Liquid Viscosity into Instantaneous Normal Modes

Viscosity, the resistance of a liquid to flow, is driven by atomic-scale friction but its microscopic origin remains poorly understood. We use a theoretical framework based on nonaffine linear response to decompose the viscosity of metallic and model liquids into contributions from individual instantaneous normal modes (INMs). Our approach reveals excellent agreement with simulations and exposes the specific excitations that govern viscous dynamics. Above the mode-coupling temperature ($T_{\text{MC}}$), viscosity is controlled by unstable localized INMs (ULINMs), which act as precursors for diffusive momentum transport. Below $T_{\text{MC}}$, we find a dynamical crossover where stable modes govern viscosity, a behavior consistent with a transition in the potential energy landscape from saddle-dominated to minima-dominated dynamics. We also propose a quantitative model connecting viscosity with ULINMs in both Arrhenius and non-Arrhenius regimes. This work provides a spectral decomposition of liquid viscosity, identifying the atomic modes responsible for it and opening a path to predict it from elementary excitations.

cond-mat.soft↗

arXiv2026

A flat-band perspective on the boson peak in amorphous solids

The boson peak is a characteristic anomaly of amorphous solids broadly defined as a low-energy excess in the density of states and heat capacity compared to the textbook predictions of Debye theory. The origin of this anomaly has long been the subject of ongoing debate and remains a topic of active controversy. We propose that the boson peak may have a defining dynamical feature: the accumulation of vibrational spectral weight within a narrow frequency window that is only weakly dependent on wavevector. In this perspective, the boson peak reflects a flat or weakly dispersive band in the dynamical structure factor rather than a propagating excitation. We revisit both experimental and simulation data from the literature through this lens and conduct further simulations in 2D and 3D amorphous systems. Taken together, these analyses provide compelling converging evidence for this interpretation and sharply constrain the space of viable theoretical descriptions of the boson peak.

cond-mat.soft↗

arXiv2026

Towards Minimal Fault-tolerant Error-Correction Sequence with Quantum Hamming Codes

The high overhead of fault-tolerant measurement sequences (FTMSs) poses a major challenge for implementing quantum stabilizer codes. Here, we address this problem by constructing efficient FTMSs for the class of quantum Hamming codes $[\![2^r-1, 2^r-1-2r, 3]\!]$ with $r=3k+1$ ($k \in \mathbb{Z}^+$). Our key result demonstrates that the sequence length can be reduced to exactly $2r+1$-only one additional measurement beyond the original non-fault-tolerant sequence, establishing a tight lower bound. The proposed method leverages cyclic matrix transformations to systematically combine rows of the initial stabilizer matrix and preserving a self-dual CSS-like symmetry analogous to that of the original quantum Hamming codes. This induced symmetry enables hardware-efficient circuit reuse: the measurement circuits for the first $r$ stabilizers are transformed into circuits for the remaining $r$ stabilizers simply by toggling boundary Hadamard gates, eliminating redundant hardware. For distance-3 fault-tolerant error correction, our approach simultaneously reduces the time overhead via shorting the FTMS length and the hardware overhead through symmetry-enabled circuit multiplexing. These results provide an important advance towards the important open problem regarding the design of minimal FTMSs for quantum Hamming codes and may shed light on similar challenges in other quantum stabilizer codes.

quant-ph↗

arXiv2025

A geometric approach to predicting plasticity in disordered solids

It was recently shown that vortex-like topological defects with negative winding number in the vibrational modes of a two-dimensional glass under quasistatic shear correlate strongly with plastic events, offering a promising route to predict them. However, many of these vortices, a number that actually grows quadratically with mode frequency, are entirely unrelated to plasticity and arise simply from the underlying plane-wave structure of the modes. This raises doubts about the fundamental relevance of such defects to plastic rearrangements and limits their predictive power. Here, we introduce a geometrical filter based on the Nye dislocation density that, when applied to the vibrational modes, removes these spurious defects and reveals the true plastic precursors. Using simulations of a two-dimensional model glass, we show that this filtered approach consistently outperforms the conventional vortex-based method, particularly at small strains and when focusing on genuine plastic stress drops, offering a more robust tool to predicting plasticity in glasses from their undeformed initial state.

cond-mat.soft↗

arXiv2025

Stress-stress correlations in two-dimensional amorphous and crystalline solids

Stress-stress correlations in crystalline solids with long-range order can be straightforwardly derived using elasticity theory. In contrast, the `emergent elasticity' of amorphous solids, rigid materials characterized by an underlying disordered structure, defies direct explanation within traditional theoretical frameworks. To address this challenge, tensor gauge theories have been recently proposed as a promising approach to describe the emergent elasticity of disordered solids and predict their stress-stress correlations. In this work, we revisit this problem in two-dimensional amorphous and crystalline solids by employing a canonical elasticity theory approach, supported by experimental and simulation data. We demonstrate that, with respect to static stress-stress correlations, the response of a 2D disordered solid is indistinguishable from that of a 2D isotropic crystalline solid and it is well predicted by vanilla elasticity theory. Moreover, we show that the presence of pinch-point singularities in the stress response is not an exclusive feature of amorphous solids. Our results confirm previous observations about the universal character of static stress-stress correlations in crystalline and amorphous packings.

cond-mat.soft↗

arXiv2025

Atomistic mechanisms of dynamics in a two-dimensional dodecagonal quasicrystal

Quasicrystals have been observed in a variety of materials ranging from metal alloys to block copolymers. However, their structural and dynamical properties cannot be readily described in terms of conventional solid-state models of liquids and solids. We may expect the dynamics of this specific class of quasicrystalline materials to be more like glass-forming liquids in the sense of exhibiting large fluctuations in the local mobility ("dynamic heterogeneity") and non-Arrhenius temperature dependence of relaxation and diffusion. In this work, we investigate a model dodecagonal quasicrystal material in two dimensions (2D) using molecular dynamics (MD) simulations, with a focus on heterogeneous dynamics and non-Arrhenius relaxation and diffusion. As observed in glass-forming liquids and heated crystals, we observe a two-stage relaxation dynamics in the self-intermediate scattering function $F_s(k,t)$ of our quasicrystal material. It involves a fast $β$-relaxation and $α$ relaxation process having a highly temperature dependent relaxation time whose activation energy varies in concert with the extent of string-like collective motion, a phenomenon recognized to occur in glass-forming liquids at low temperatures and crystalline materials at elevated temperatures. After examining the dynamics of our dodecagonal quasicrystalline material in great detail, we conclude that the dynamics of these materials more closely resembles observations on metallic glass-forming liquids than crystalline materials.

cond-mat.mtrl-sci↗

arXiv2024

Spotting structural defects in crystals from the topology of vibrational modes

Because of the inevitably disordered background, structural defects are not well-defined concepts in amorphous solids. In order to overcome this difficulty, it has been recently proposed that topological defects can be still identified in the pattern of vibrational modes, by looking at the corresponding eigenvector field at low frequency. Moreover, it has been verified that these defects strongly correlate with the location of soft spots in glasses, that are the regions more prone to plastic rearrangements. Here, we show that the topology of vibrational modes predicts the location of structural defects in crystals as well, including the cases of dislocations, disclinations and Eshelby inclusions. Our results suggest that in crystalline solids topological defects in the vibrational modes are directly connected to the well-established structural defects governing plastic deformations and present characteristics very similar to those observed in amorphous solids.

cond-mat.mtrl-sci↗

arXiv2024

Quantum resource theory of coding for error correction

Error-correction codes are central for fault-tolerant information processing. Here we develop a rigorous framework to describe various coding models based on quantum resource theory of superchannels. We find, by treating codings as superchannels, a hierarchy of coding models can be established, including the entanglement assisted or unassisted settings, and their local versions. We show that these coding models can be used to classify error-correction codes and accommodate different computation and communication settings depending on the data type, side channels, and pre-/postprocessing. We believe the coding hierarchy could also inspire new coding models and error-correction methods.

quant-ph↗

arXiv2022

Short-range order and its impacts on the BCC NbMoTaW multi-principal element alloy by the machine-learning potential

We employ a machine-learning force field, trained by a neural network (NN) with bispectrum coefficients as descriptors, to investigate the short-range order (SRO) influences on the BCC NbMoTaW alloy strengthening mechanism. The NN interatomic potential provides a transferable force field with density functional theory accuracy. This novel NN potential is applied to elucidate the SRO effects on the elasticity, vibrational modes, plasticity, and strength in the NbMoTaW multi-principal element alloy (MPEA). The results show the strong attraction among Mo-Ta pairs forming the local ordered B2 structures, which could be tuned via temperature and improved by Nb content. SRO increases the elastic constants and high-frequency phonon modes as well as introduces extra lattice friction of dislocation motion. This approach enables a rapid compositional screening, paves the way for computation-guided materials design of new MPEAs with better performance, and opens avenues for tuning the mechanical properties by processing optimization.

cond-mat.mtrl-sci↗

arXiv2022

Hidden spatiotemporal sequence in transition to shear band in amorphous solids

Shear banding is a fundamental non-equilibrium phenomenon in amorphous solids. Due to the intrinsic entangling of three local atomic motions: shear, dilatation and rotation, the precise physical process of shear band emergence is still an enigma. To unveil this mystery, we formulate for the first time a theoretical protocol covering both affine and non-affine components of deformation, to decode these highly entangled local atomic-scale events. In contrast to the broad concept of shear transformation zone, plastic behavior can be demonstrated comprehensively as the operative manipulation of more exact shear-dominated zones (SDZs), dilatation-dominated zones (DDZs) and rotation-dominated zones (RDZs). Their spatiotemporal evolution exhibits a novel transition from synchronous motion to separate distribution at the onset of shear band, which is in striking resemblance with the transition from laminar flow to turbulent flow in flow dynamics. The hidden mechanism is revealed with the help of extreme value theory (EVT) and percolation analysis. Analysis of EVT indicates dilatation is the dominant mode at the embryo of initial plastic units. The percolation analysis points towards the critical power-law scaling nature at the transition from stochastic activation to percolation of plastic regions. Then the comprehensive pictures of shear banding emergence are uncovered. Firstly, dilatation triggers initial shear and rotation in soft regions, leading to embryo of flow units, which is followed by the inhomogeneous turbulent-like pattern manifesting as the secondary activation of rotation in neighboring hard material. Such rotation activation contributes to further perturbation, and ultimately, leads to shear band formation. Our findings also reinforce that the discussion of plastic behavior in disordered materials must take into account both affine and non-affine component deformation.

cond-mat.dis-nn↗

arXiv2022

Correlation between vibrational anomalies and emergent anharmonicity of local potential energy landscape in metallic glasses

The boson peak (BP) is a universal feature in the Raman and inelastic scattering spectra of both disordered and crystalline materials. The current paradigm presents the boson peak as the result of a Ioffe-Regel crossover between ballistic (phonon) and diffusive-type excitations, where the loss of coherence of phonons is described as a purely harmonic process due to structural disorder. This "harmonic disorder" paradigm for the BP has never been challenged or tested at the atomistic level. Here, through a set of atomistically-resolved characterizations of amorphous metallic alloys, we uncover a robust inverse proportionality between the intensity of boson peak and the activation energy of excitations in the potential energy landscape (PEL). Larger boson peak is linked with shallower basins and lower activation barriers and, consequently, with strongly anharmonic sectors of the PEL. Numerical evidence from atomistic simulations indicates that THz atomic vibrations contributing the most to the BP in atomic glasses are strongly anharmonic, as evidenced through very large values of the atomic- and mode-resolved Grüneisen parameter found for the atomic vibrations that constitute the BP. These results provide a direct bridge between the vibrational spectrum and the topology of the PEL in solids, and point towards a new "giant anharmonicity" paradigm for both generic disordered materials and for the phonon-glass problem in emerging materials for energy applications. In this sense, disorder and anharmonicity emerge as the two sides of the same coin.

cond-mat.dis-nn↗

arXiv2021

Theory of quasi-exact fault-tolerant quantum computing and valence-bond-solid codes

In this work, we develop the theory of quasi-exact fault-tolerant quantum (QEQ) computation, which uses qubits encoded into quasi-exact quantum error-correction codes ("quasi codes"). By definition, a quasi code is a parametric approximate code that can become exact by tuning its parameters. The model of QEQ computation lies in between the two well-known ones: the usual noisy quantum computation without error correction and the usual fault-tolerant quantum computation, but closer to the later. Many notions of exact quantum codes need to be adjusted for the quasi setting. Here we develop quasi error-correction theory using quantum instrument, the notions of quasi universality, quasi code distances, and quasi thresholds, etc. We find a wide class of quasi codes which are called valence-bond-solid codes, and we use them as concrete examples to demonstrate QEQ computation.

quant-ph↗

arXiv2020

Atomistic structural mechanism for the glass transition: Entropic contribution

A popular Adam--Gibbs scenario has suggested that the excess entropy of glass and liquid over crystal dominates the dynamical arrest at the glass transition with exclusive contribution from configurational entropy over vibrational entropy. However, an intuitive structural rationale for the emergence of frozen dynamics in relation to entropy is still lacking. Here we study these issues by atomistically simulating the vibrational, configurational, as well as total entropy of a model glass former over their crystalline counterparts for the entire temperature range spanning from glass to liquid. Besides confirming the Adam--Gibbs entropy scenario, the concept of Shannon information entropy is introduced to characterize the diversity of atomic-level structures, which undergoes a striking variation across the glass transition, and explains the change found in the excess configurational entropy. Hence, the hidden structural mechanism underlying the entropic kink at the transition is revealed in terms of proliferation of certain atomic structures with a higher degree of centrosymmetry, which are more rigid and possess less nonaffine softening modes. In turn, the proliferation of these centrosymmetric (rigid) structures leads to the freezing-in of the dynamics beyond which further structural rearrangements become highly unfavourable, thus explaining the kink in the configurational entropy at the transition.

cond-mat.soft↗

arXiv2018

Assessing the Utility of Structure in Amorphous Materials

This paper presents a set of general strategies for the analysis of structure in amorphous materials and a general approach to assessing the utility of a selected structural description. Measures of structural diversity and utility are defined and applied to two model glass forming binary atomic alloys. In addition, a new measure of incipient crystal-like organization is introduced, suitable for cases where the stable crystal is a compound structure.

cond-mat.soft↗

arXiv2018

Incorporating a soft ordered phase into an amorphous configuration enhances its uniform plastic deformation under shear

Amorphous materials of homogeneous structures usually suffer from nonuniform deformation under shear, which can develop into shear localization and eventually destructive shear band. One approach to tackle this issue is to introduce an inhomogeneous structure containing more than one phase, which can reduce the local nonuniform shear deformation and hinder its percolation throughout the system. Using thermostated molecular dynamics (MD) simulations, we compare the deformation behavior between a homogeneous amorphous mixture of bidisperse disc particles, interacting via an n-6 Lennard-Jones potential of tunable softness, with an inhomogeneous one containing an evenly-distributed ordered phase. We change the population ratio of large to small particles to create a homogeneous or an inhomogeneous mixture, where the softness of a chosen phase can be manually adjusted by specifying n of the interparticle potential. Results of applying extensive quasistatic shear on the prepared mixtures reveal that the inhomogeneous amorphous mixture containing a soft ordered phase overall deforms more uniformly than the homogeneous one, which indicates that both the structure inhomogeneity and the inter-phase softness variance play important roles in enhancing the uniformity of the plastic deformation under shear.

cond-mat.mtrl-sci↗

arXiv2017

Atomic theory of viscoelastic response and memory effects in metallic glasses

An atomic-scale theory of the viscoelastic response of metallic glasses is derived from first principles, using a Zwanzig-Caldeira-Leggett system-bath Hamiltonian as a starting point within the framework of nonaffine linear response to mechanical deformation. This approach provides a Generalized-Langevin-Equation (GLE) as the average equation of motion for an atom or ion in the material, from which non-Markovian nonaffine viscoelastic moduli are extracted. These can be evaluated using the vibrational density of states (DOS) as input, where the boson peak plays a prominent role for the mechanics. To compare with experimental data of binary ZrCu alloys, numerical DOS was obtained from simulations of this system, which take also electronic degrees of freedom into account via the embedded atom method (EAM) for the interatomic potential. It is shown that the viscoelastic $α$-relaxation, including the $α$-wing asymmetry in the loss modulus, can be very well described by the theory if the memory kernel (the non-Markovian friction) in the GLE is taken to be a stretched-exponential decaying function of time. This finding directly implies strong memory effects in the atomic-scale dynamics, and suggests that the $α$-relaxation time is related to the characteristic time-scale over which atoms retain memory of their previous collision history. This memory time grows dramatically below the glass transition.

cond-mat.soft↗