softwareQinc/qpp

Quantum++ (qpp) is a mature (12-year-old) and stable library in the quantum software ecosystem. With 650 stars and 139 forks, it has established itself as a reliable tool for researchers who require low-level C++ performance rather than the higher-level abstractions provided by Python-centric frameworks like Qiskit or Cirq. Its moat is built on its comprehensive implementation of quantum information theory primitives (density matrices, multipartite systems, and sophisticated noise models) and its efficient use of the Eigen template library. Unlike gate-only simulators, qpp is a general-purpose toolbox for quantum math. It faces little risk from frontier AI labs (OpenAI/Anthropic), as the domain is too specialized and mathematically intensive to be a priority for LLM providers. The primary threat comes from the shift toward GPU-accelerated simulation (e.g., NVIDIA cuQuantum) and the consolidation of the quantum industry around a few dominant SDKs that may eventually integrate similar low-level C++ capabilities, potentially making standalone libraries less necessary for non-specialists. However, its longevity and deep integration into academic research projects provide significant staying power.