arXiv subjects

Kevin Wen

Publications and source records attributed to Kevin Wen.

4 recordsLinked to original sources

arXiv2026

MathNet: a Global Multimodal Benchmark for Mathematical Reasoning and Retrieval

Mathematical problem solving remains a challenging test of reasoning for large language and multimodal models, yet existing benchmarks are limited in size, language coverage, and task diversity. We introduce MathNet, a high-quality, large-scale, multimodal, and multilingual dataset of Olympiad-level math problems together with a benchmark for evaluating mathematical reasoning in generative models and mathematical retrieval in embedding-based systems. MathNet spans 47 countries, 17 languages, and two decades of competitions, comprising 30,676 expert-authored problems with solutions across diverse domains. In addition to the core dataset, we construct a retrieval benchmark consisting of mathematically equivalent and structurally similar problem pairs curated by human experts. MathNet supports three tasks: (i) Problem Solving, (ii) Math-Aware Retrieval, and (iii) Retrieval-Augmented Problem Solving. Experimental results show that even state-of-the-art reasoning models (78.4% for Gemini-3.1-Pro and 69.3% for GPT-5) remain challenged, while embedding models struggle to retrieve equivalent problems. We further show that retrieval-augmented generation performance is highly sensitive to retrieval quality; for example, DeepSeek-V3.2-Speciale achieves gains of up to 12%, obtaining the highest scores on the benchmark. MathNet provides the largest high-quality Olympiad dataset together with the first benchmark for evaluating mathematical problem retrieval, and we publicly release both the dataset and benchmark at https://mathnet.mit.edu.

cs.AI↗

arXiv2026

Enhanced Interband Optical Nonlinearities from Coupled Quantum Wells

The recent, rapid advances in nonlinear chipscale nanophotonics in the visible and near-infrared have been largely driven by manipulating the local dielectric environment proximate to decades-old workhorse bulk nonlinear optical materials, rather than increasing the inherent strength of their nonlinear response. While proposed decades ago, we demonstrate the first experimental realization of a new class of designer nonlinear materials that leverage the interband optical transition in asymmetric structures to provide strong second order susceptibility, $\chi^{(2)}$. Using simple AlGaAs/GaAs coupled quantum wells operating in the near-infrared as a prototype, we observed strong second harmonic generation enhancement of 1550 nm to 775 nm over bulk controls. Extracted $\chi^{(2)}$ values were as high as 2750 pm/V, which is $>$7x that of bulk GaAs. Furthermore, measured susceptibilities agreed well with quantum mechanical calculations of $\chi^{(2)}$ using layer profiles extracted from electron microscopy. Growth interruptions were employed to improve interfacial abruptness in response to electron microscopy characterization, resulting in increased $\chi^{(2)}$ toward the simulation predictions for ideal heterointerfaces. More complex layer designs showed predicted $\chi^{(2)}$ up to 7 nm/V. Such materials are anticipated to find myriad applications, including entangled photon generation at telecommunications wavelengths for chipscale quantum information processing.

physics.optics↗

arXiv2025

Thermal and thermoelectric transport in flat bands with non-trivial quantum geometry

Although quasiparticles in flat bands have zero group velocity, they can display an anomalous velocity due to the quantum geometry. We address the thermal and thermoelectric transport in flat bands in the clean limit with a small amount of broadening due to inelastic scattering. We derive general Kubo formulas for flat bands in the DC limit up to linear order in the broadening and extract expressions for the thermal conductivity, the Seebeck and Nernst coefficients. We show that the Seebeck coefficient for flat Chern bands is topological up to second order corrections in the broadening. We identify thermal and thermoelectric transport signatures for two generic flat Chern bands and also for the generalized flattened Lieb model, which describes a family of three equally spaced flat Chern bands where the middle one is topologically trivial. Finally, we address the saturation of the quantum metric lower bound for a general family of Hamiltonians with an arbitrary number of flat Chern bands corresponding to SU(2) coherent states. We find that only the extremal bands in this class of Hamiltonians saturate the bound, provided that the momentum dependence of their Hamiltonians is described by a meromorphic function.

cond-mat.mes-hall↗

arXiv2024

Monte-Carlo simulations of the capture and cooling of alkali-metal atoms by a supersonic helium jet

We present three-dimensional Monte-Carlo simulations of the capture of 1000 K $^7$Li or 500 K $^{87}$Rb atoms by a continuous supersonic $^4$He jet and show that intense alkali-metal beams form with narrow transverse and longitudinal velocity distributions. The nozzle creating the $^4$He jet is held at approximately 4 K. These conditions are similar to those in the cold $^7$Li source developed by some of us as described in [Phy. Rev. A 107, 013302 (2023)]. The simulations use differential cross-sections obtained from quantum scattering calculations of $^7$Li or $^{87}$Rb atoms with $^4$He atoms for relative collision energies between $k\times 1$ mK to $k\times 3000$ K, where $k$ is the Boltzmann constant. For collision energies larger than $\approx k\times 4$ K the collisions favor forward scattering, deflecting the $^7$Li or $^{87}$Rb atoms by no more than a few degrees. From the simulations, we find that about 1$\%$ of the lithium atoms are captured into the $^4$He jet, resulting in a lithium beam with a most probable velocity of about $210$ m/s and number densities on the order of $10^{8}$ cm$^{-3}$. Simulations predict narrow yet asymmetric velocity distributions which are verified by comparing to fluorescence measurements of the seeded $^7$Li atoms. We find agreement between simulated and experimentally measured seeded $^7$Li densities to be better than 50$\%$ across a range of $^4$He flow rates. We make predictions for capture efficiency and cooling of $^{87}$Rb by a supersonic $^4$He jet. The capture efficiency for $^{87}$Rb is expected to be similar to $^7$Li.

physics.atom-ph↗