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<header class="site-header"><nav aria-label="Main navigation"><a href="index.html">Overview</a><a href="about.html">Background</a><a href="publications.html">Publications</a><a aria-current="page" href="projects.html">Projects</a><a href="blog.html">Notes</a><a href="contact.html">Contact</a></nav><div aria-label="Language" class="language-switch" translate="no"><a aria-current="true" href="projects.html" hreflang="en" lang="en">English</a><a href="zh/projects.html" hreflang="zh-Hans" lang="zh-Hans">简体中文</a></div></header>
<main id="main"><section class="page-hero"><p class="eyebrow" data-i18n="projects.block01">ENGINEERING / OPEN SOURCE</p><h1 data-i18n="projects.block02">Projects &amp; software.</h1><p class="intro" data-i18n="projects.block03">C++ tools for scientific computing and performance-sensitive systems. Each project explores a specific computational problem, with source code and implementation details on GitHub.</p></section><section class="section"><div class="project-grid"><article class="project-card" data-i18n-scope="project-QLeaf"><p class="eyebrow" data-i18n="project.QLeaf.category">01 / SYSTEMS &amp; MACHINE LEARNING</p><h3><a href="https://github.com/LiJ21/QLeaf" rel="noopener noreferrer" target="_blank">QLeaf ↗</a></h3><p class="project-subtitle" data-i18n="project.QLeaf.subtitle">Low-latency tree inference</p><p data-i18n="project.QLeaf.description">A low-latency tree inference framework, reaching single-digit microsecond latency for hundreds to thousands of shallow trees.</p><p class="project-detail" data-i18n="project.QLeaf.detail">QLeaf aggressively optimizes data transfer and cross-block coordination, and uses a lock-free host–device handoff to bring end-to-end latency close to the limits of host–device communication.</p><ul aria-label="Technologies" class="tags"><li>C++</li><li>CUDA</li><li>CPU / GPU</li></ul><div class="project-links"><a href="https://github.com/LiJ21/QLeaf" rel="noopener noreferrer" target="_blank">Repository ↗</a><a href="https://github.com/LiJ21/QLeaf/blob/main/BENCHMARK.md" rel="noopener noreferrer" target="_blank">Benchmarks ↗</a></div></article><article class="project-card" data-i18n-scope="project-QuDrip"><p class="eyebrow" data-i18n="project.QuDrip.category">02 / COMPUTATIONAL PHYSICS</p><h3><a href="https://github.com/LiJ21/QuDrip" rel="noopener noreferrer" target="_blank">QuDrip ↗</a></h3><p class="project-subtitle" data-i18n="project.QuDrip.subtitle">Exact quantum many-body simulation</p><p data-i18n="project.QuDrip.description">A toolbox for constructing constrained Hilbert spaces, quantum operators, and Hamiltonians. Sparse-matrix and Krylov methods support ground-state calculations, real-time evolution, and Lindblad dynamics.</p><p class="project-detail" data-i18n="project.QuDrip.detail">Designed for flexible small-to-medium quantum systems, including fermionic and bosonic degrees of freedom. Used in research on quantum-light control and photodoped superconductivity.</p><ul aria-label="Technologies" class="tags"><li>C++</li><li>Eigen</li><li>Krylov methods</li></ul><div class="project-links"><a href="https://github.com/LiJ21/QuDrip" rel="noopener noreferrer" target="_blank">Repository ↗</a><a href="publications.html#paper-03">Related publication →</a></div></article><article class="project-card" data-i18n-scope="project-OptIndex"><p class="eyebrow" data-i18n="project.OptIndex.category">03 / DATA STRUCTURES</p><h3><a href="https://github.com/LiJ21/OptIndex" rel="noopener noreferrer" target="_blank">OptIndex ↗</a></h3><p class="project-subtitle" data-i18n="project.OptIndex.subtitle">Safe intrusive object store</p><p data-i18n="project.OptIndex.description">A safe intrusive object store with stable addresses and compile-time index definitions. Centralized storage and object lifetime management keep optional or partitioned views consistent without duplicating objects.</p><p class="project-detail" data-i18n="project.OptIndex.detail">Built for bounded working sets and repeated queries, with explicit indexing control and an optional fixed-size pool. The design addresses consistency across indices without duplicating the stored objects.</p><ul aria-label="Technologies" class="tags"><li>C++</li><li>Boost.Intrusive</li><li>Memory management</li></ul><div class="project-links"><a href="https://github.com/LiJ21/OptIndex" rel="noopener noreferrer" target="_blank">Repository ↗</a></div></article><article class="project-card" data-i18n-scope="project-RL Tools"><p class="eyebrow" data-i18n="project.RL Tools.category">04 / LEARNING ALGORITHMS</p><h3><a href="https://github.com/LiJ21/rl_tools" rel="noopener noreferrer" target="_blank">RL Tools ↗</a></h3><p class="project-subtitle" data-i18n="project.RL Tools.subtitle">Composable reinforcement learning</p><p data-i18n="project.RL Tools.description">A lightweight reinforcement learning framework that separates agents from their value models. SARSA and Q-learning agents work with tabular storage or Torch-based function approximators.</p><p class="project-detail" data-i18n="project.RL Tools.detail">Template-based interfaces keep the interaction loop small: observe a state, select an action, and collect a reward. Core components are header-only; neural models use LibTorch.</p><ul aria-label="Technologies" class="tags"><li>C++</li><li>Templates</li><li>LibTorch</li></ul><div class="project-links"><a href="https://github.com/LiJ21/rl_tools" rel="noopener noreferrer" target="_blank">Repository ↗</a></div></article><article class="project-card" data-i18n-scope="project-NESSi 2.0"><p class="eyebrow" data-i18n="project.NESSi 2.0.category">05 / COLLABORATIVE RESEARCH SOFTWARE</p><h3><a href="https://github.com/nessi-cntr/nessi" rel="noopener noreferrer" target="_blank">NESSi 2.0 ↗</a></h3><p class="project-subtitle" data-i18n="project.NESSi 2.0.subtitle">Nonequilibrium systems simulation</p><p data-i18n="project.NESSi 2.0.description">A shared research library for nonequilibrium Green’s functions and interacting quantum systems. Version 2.0 adds memory-truncated time propagation and steady-state calculations.</p><p class="project-detail" data-i18n="project.NESSi 2.0.detail">I contributed to the development of NESSi 2.0 through my research on nonequilibrium many-body methods. The package supports accurate numerical integration and distributed-memory calculations for quantum dynamics.</p><ul aria-label="Technologies" class="tags"><li>C++</li><li>Green’s functions</li><li>DMFT</li></ul><div class="project-links"><a href="https://github.com/nessi-cntr/nessi" rel="noopener noreferrer" target="_blank">Repository ↗</a><a href="publications.html#paper-33">NESSi 2.0 paper →</a></div></article></div><div class="inline-links"><a href="https://github.com/LiJ21" rel="noopener noreferrer" target="_blank">All GitHub repositories ↗</a></div></section>
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