Keyboard shortcuts

Press ← or → to navigate between chapters

Press S or / to search in the book

Press ? to show this help

Press Esc to hide this help

Roadmap & milestones

This page tracks status and is updated as each milestone lands. The rationale for the order is in How we optimize.

Status

VerMilestoneStatus
v0.0scaffold + naive RefBackend oracle + correctness tests✅ done
v0.1ReshapeBackend — block / out-of-place apply✅ done
v0.2BitShiftBackend — in-place bit-shift pair kernel✅ done
v0.3CpuBackend — bounds-check-free access + stack gate matrices✅ done
v0.4CpuBackend — cache-friendly nested-block 1q kernel✅ done
v0.5CpuBackend::parallel() — rayon threading✅ done
v0.6CpuBackend — diagonal-gate fast path✅ done
v0.7SimdBackend — portable wide::f64x4 1q kernel✅ done (null result¹)
v0.8gate fusion (fusion::fuse)✅ done
v0.9cache-block the multi-qubit kernel + prefetch + NT stores⬜ next²
v0.10ILP, x86 BMI2, alias-table sampling, parallel prefix-sum⬜
v1.0roofline-validated, documented, cross-sim benchmarked⬜

¹ SIMD measured ~0% on the 1q kernel — it's bandwidth-bound, not arithmetic-bound. See benchmarking. Expected to matter for fused multi-qubit matvecs and x86 AVX-512. ² Promoted to "next" by the v0.8 finding: fusion's win is currently capped at large N by the multi-qubit kernel's scattered access — cache-blocking it is the unlock.

Also planned but out of the v1 critical path: density-matrix / noise simulation, a GPU backend (CUDA/cuTile or Metal) behind the Backend seam, and distributed multi-node support (mirroring QuEST's pairwise rank exchange).

Testing

Robustness rests on differential testing: every optimized backend must reproduce the naive RefBackend oracle amplitude-for-amplitude. Because the oracle is implemented a structurally different way (gather/scatter, not the bit-shift pairing), this genuinely cross-checks the kernels rather than re-running the same logic.

Current suite (grows with each milestone):

  • 200 reproducible random circuits (3–8 qubits, depth 20–60) — every optimized backend (Reshape, BitShift, CpuBackend serial and parallel) vs oracle;
  • 15 random circuits at 10 qubits, depth 80 — BitShiftBackend vs oracle;
  • 6 random circuits at 14 qubits (above the threading threshold) — CpuBackend's rayon path, including the multi-qubit parallel kernel, vs oracle;
  • QFT → uniform superposition (n = 1,2,3,5,8) and QFT vs oracle;
  • a 3-qubit Toffoli across several qubit orderings, exercising the general apply_mq path;
  • unit tests for the index arithmetic (pairs differ in exactly the target bit; block anchors tile the space) and for the RNG/generators.

Every kernel added in a later milestone is wired into this same differential harness, so the optimization can never silently break correctness.

Definition of done for a milestone

  1. New backend (or kernel) implemented behind the Backend trait.
  2. Differential tests against the oracle pass, including any new path it introduces.
  3. cargo clippy --all-targets -- -D warnings and cargo fmt --check clean.
  4. A benchmark data point recorded (see Benchmarking & profiling).
  5. This roadmap and the relevant design pages updated.