wai-quantum 0.3.26: tensor-network contraction, hyper-optimised, sliced, bit-identical #144

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2026-10-04

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wai-quantum 0.3.26: tensor-network contraction, hyper-optimised, sliced, bit-identical ...

quantum_tn turns a circuit (any unitary on any qubits, as a matrix) into the
tensor network of one amplitude or an open-output batch, and contracts it.

- Network::amplitude builds the network; simplify absorbs vectors and
  one-qubit gates into neighbours.
- find_path is a seeded hyper-optimiser over two tree families:
  - randomised greedy, scoring size(out)/c - c(size(a)+size(b)) with Gumbel
    noise;
  - recursive bipartition, multilevel (heavy-edge coarsening, several
    initial cuts, refinement at every level), with greedy leaves.
  Families alternate until one leads; later trials sample near the best
  parameters. The best few trees are reconfigured: subtrees of up to eight
  tensors are re-contracted optimally by subset dynamic programming, until
  nothing improves.
- slice fixes the index that leaves the least total work until the largest
  intermediate fits the cap, pricing each candidate incrementally. A second
  search round then finds a tree for the network with the first round's
  slices fixed (all, or the more valuable half).
- contract_plan contracts every slice in a fixed accumulation order and sums
  them in order. Threads are bounded by an 8 GiB budget; WASI runs
  sequentially. The bits are the same everywhere.

Measured on single amplitudes of random circuits on the 54-qubit
advantage-experiment grid (fSim(pi/2, pi/6), staggered couplers), 256 trials,
under ten seconds each, in log10 operations:
  m = 10: 10.48   m = 12: 13.91   m = 14: 14.63   m = 16: 17.60   m = 20: 18.77
An independently developed hyper-optimiser, given the identical networks,
lands within 0.4 of these at every depth, in either direction. The 54-qubit,
10-cycle amplitude, contracted here in 16 slices, agrees with an independent
contraction to 12 significant figures.

Tests:
- Amplitudes match a dense state vector for every tree family, with
  reconfiguration and with slicing.
- Reconfiguration reaches the exact optimum on 40 random small networks.
- Incremental slice pricing matches a full recount.
- The same seed gives the same plan.
- Mutating the permutation, the complex product, the contraction's summed
  indices, slice pricing, the slice offset or the reconfiguration DP fails a
  named test.
- bit_identity pins a plan and its sliced, threaded amplitude natively and
  under wasm32-wasip2.

CLI: wai-quantum tn --file CIRCUIT.jsonl [--bits --open --trials --seed
--cap-log2 --plan-only --json], byte-identical natively and under
wasm32-wasip2.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

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