Architecture: Overview and Layered Design

This section is the technical reference for how PRISM-Q is built. See the Glossary for definitions of terms used throughout.

Goals

• Primary: Fastest practical quantum circuit simulation in Rust.
• Correct simulation of supported gate sets across multiple backend strategies.
• Clean backend plugin model. New simulation strategies can be added without touching the core.

Non-goals

• Full OpenQASM 3.0 compliance (supports a practical subset).
• GUI or notebook integration (library-first).
• Hardware backend / QPU connectivity.

Layered design

A circuit flows top to bottom: text is parsed into a backend-agnostic IR, optimized by the fusion pipeline, then dispatched by the simulation engine to one of the backends or a compiled sampler.

flowchart TD
    U[User / Application]
    API["Public API — run_qasm, simulate (src/lib.rs)"]
    P["OpenQASM 3.0 Parser — &str to Circuit IR (src/circuit/openqasm.rs)"]
    IR["Circuit IR — gates, measures, barriers, conditionals (src/circuit/mod.rs)"]
    F["Fusion Pipeline — cancel, fuse, reorder, batch (src/circuit/fusion.rs)"]
    E["Simulation Engine — dispatch, decompose, execute (src/sim/mod.rs)"]
    U --> API --> P --> IR --> F --> E
    E --> B[Backends]
    E --> C["Compiled Samplers — shot-based (src/sim/compiled, noise.rs, homological.rs)"]
    B --> SV[Statevector]
    B --> TN[Tensor Network]
    B --> MPS[MPS]
    B --> SP[Sparse]
    B --> PR[Product]
    B --> ST[Stabilizer]
    B --> FA[Factored]

The remaining pages in this section follow that flow: the parser and circuit IR, the fusion pipeline, the simulation engine and dispatch, the individual backends, the compiled samplers, the native QEC program IR, the threading, SIMD, and memory layout, and the error model and public API surface.