wai-quantum 0.6.7: tensor networks that split controlled gates and fix projections #343

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dcharlot merged 3 commits from wai/quantum-tn-split-0.6.7 into main 2026-10-19 22:37:45 -04:00

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dcharlot commented 2026-10-19 20:36:27 -04:00

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wai-quantum 0.6.7. Two exact network reductions that cut the cost of controlled-Z and controlled-X circuits by orders of magnitude.

What changes

• Network::amplitude_split splits each gate on two or more qubits at every qubit it is block-diagonal on: a control, or a qubit it is diagonal on.
  • There G = Σ_a |a⟩⟨a| ⊗ G_a, so that qubit's part is the delta δ(out, in, k) on its wire, and the blocks G_k keep the rest, joined by a bond of dimension 2.
  • Only zeros of the matrix are read, with no arithmetic.
  • A cut through a CZ or CX costs 2 instead of the 4 of its two wires, and a cut crossed by m such gates costs 2^m less.
• Network::reduce fixes every index that some tensor allows only one value of.
  • Every tensor holding that index keeps its entries at that value and drops the index; this repeats until nothing changes, then it simplifies.
  • Input and output projections run through diagonal gates and split deltas, so a CZ beside a projected output becomes scalars.
  • Open indices are never fixed.
• Network::amplitude and Network::simplify are unchanged, so every pinned digest is too (tests/bit_identity: 23 passed).
• Callers moved to split, reduced networks:
  • examples/tn_cost (TN_DENSE=1 for the old pipeline);
  • the CLI's wai-quantum tn (--whole-gates);
  • the service's tensor_network method.

Measured

On a published release's 61-qubit CZ circuits: log₁₀ multiply-adds for one amplitude, 64 trials.

depth	whole gates, simplified	split	split, reduced
8	8.03	6.58	5.35
12	12.46	9.23	8.25
16	16.09	12.09	11.22
20	19.64	15.16	14.26

1,024 trials do not lower the split costs further.

Tests

• Split networks, reduced or not, and reduced whole-gate networks give the state vector's amplitudes. The circuits mix CZ, CX both ways, a controlled random unitary, random diagonal gates, Toffoli, CCZ and random two-qubit unitaries, and the outputs are both projected and open.
• CZ and CX split, a random unitary does not, and CX splits at its control.
• On a 4 × 5 CZ grid of 12 layers, the split tree costs under an eighth of the whole-gate one.
• Mutants caught: the delta's entry, the block-diagonal test, and the value reduce keeps.
• Checked on the build host:
  • check-lockfiles;
  • cargo test --release --features full --lib quantum_tn (13 passed), --test tn_vs_sv, --test bit_identity;
  • the service's tests (60 passed);
  • cargo check of the CLI binary;
  • clippy reports nothing in the touched files.
• The public-text checks are clean.

🤖 Generated with Claude Code

**wai-quantum 0.6.7.** Two exact network reductions that cut the cost of controlled-Z and controlled-X circuits by orders of magnitude. ### What changes - **`Network::amplitude_split`** splits each gate on two or more qubits at every qubit it is block-diagonal on: a control, or a qubit it is diagonal on. - There `G = Σ_a |a⟩⟨a| ⊗ G_a`, so that qubit's part is the delta `δ(out, in, k)` on its wire, and the blocks `G_k` keep the rest, joined by a bond of dimension 2. - Only zeros of the matrix are read, with no arithmetic. - A cut through a CZ or CX costs 2 instead of the 4 of its two wires, and a cut crossed by m such gates costs 2^m less. - **`Network::reduce`** fixes every index that some tensor allows only one value of. - Every tensor holding that index keeps its entries at that value and drops the index; this repeats until nothing changes, then it simplifies. - Input and output projections run through diagonal gates and split deltas, so a CZ beside a projected output becomes scalars. - Open indices are never fixed. - **`Network::amplitude` and `Network::simplify` are unchanged**, so every pinned digest is too (`tests/bit_identity`: 23 passed). - **Callers moved to split, reduced networks:** - `examples/tn_cost` (`TN_DENSE=1` for the old pipeline); - the CLI's `wai-quantum tn` (`--whole-gates`); - the service's `tensor_network` method. ### Measured On a published release's 61-qubit CZ circuits: log₁₀ multiply-adds for one amplitude, 64 trials. | depth | whole gates, simplified | split | split, reduced | |---|---|---|---| | 8 | 8.03 | 6.58 | 5.35 | | 12 | 12.46 | 9.23 | 8.25 | | 16 | 16.09 | 12.09 | 11.22 | | 20 | 19.64 | 15.16 | 14.26 | 1,024 trials do not lower the split costs further. ### Tests - Split networks, reduced or not, and reduced whole-gate networks give the state vector's amplitudes. The circuits mix CZ, CX both ways, a controlled random unitary, random diagonal gates, Toffoli, CCZ and random two-qubit unitaries, and the outputs are both projected and open. - CZ and CX split, a random unitary does not, and CX splits at its control. - On a 4 × 5 CZ grid of 12 layers, the split tree costs under an eighth of the whole-gate one. - **Mutants caught:** the delta's entry, the block-diagonal test, and the value `reduce` keeps. - **Checked on the build host:** - `check-lockfiles`; - `cargo test --release --features full --lib quantum_tn` (13 passed), `--test tn_vs_sv`, `--test bit_identity`; - the service's tests (60 passed); - `cargo check` of the CLI binary; - clippy reports nothing in the touched files. - The public-text checks are clean. 🤖 Generated with [Claude Code](https://claude.com/claude-code)

dcharlot added 3 commits 2026-10-19 20:36:27 -04:00

wai-quantum tn: split controlled and diagonal gates at their block-diagonal qubits ... 36b1137a23

Network::amplitude_split builds the same network as Network::amplitude but
splits each gate on two or more qubits at every qubit it is block-diagonal on
(a control, or a qubit it is diagonal on): G = Σ_a |a⟩⟨a| ⊗ G_a becomes the
delta δ(out, in, k) on that qubit's wire and the blocks G_k, joined by a bond
of dimension 2. Only zeros of the matrix are read, so the amplitudes are the
same entries' sums. A cut through a CZ or CX then costs 2, not 4.

On the 61-qubit CZ circuits of a published release, depth 8/12/16/20, the
search (64 trials) finds log10 multiply-adds 6.58/9.23/12.09/15.16 on split
networks against 8.03/12.46/16.09/19.64 on whole-gate ones. 1024 trials do not
lower them further.

tn_cost, the wai-quantum CLI's tn subcommand (--whole-gates for the old
networks) and the service's tensor_network method build split networks.

Tests: split networks give the state vector's amplitudes on circuits of CZ,
CX both ways, a controlled random unitary, random diagonal gates, Toffoli,
CCZ and random two-qubit unitaries, with outputs projected and open; CZ and
CX split and a random unitary does not, CX at its control; on a 4 × 5 CZ grid
of 12 layers the split network's tree costs less than an eighth of the
whole-gate one's.

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

wai-quantum tn: Network::reduce fixes the indices a tensor allows one value of ... 382cf672a2

Where a tensor is zero unless index i takes v, every tensor holding i keeps
its entries at v and drops i, repeated until nothing changes; then simplify.
Only zeros are read and entries selected. Projections run through diagonal
gates and the deltas of split ones, so a CZ beside a projected output becomes
scalars. Open indices are never fixed. simplify itself is unchanged, so
networks that do not call reduce keep their bits.

On the same 61-qubit CZ circuits (depth 8/12/16/20, 64 trials): log10
multiply-adds 5.35/8.25/11.22/14.26 split and reduced, against 6.58/9.23/
12.09/15.16 split alone and 8.03/12.46/16.09/19.64 whole and simplified.

tn_cost, the CLI's tn subcommand and the service's tensor_network method
reduce their split networks. Tests: split networks reduced, and whole-gate
networks reduced, give the state vector's amplitudes; open outputs too.

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

wai-quantum 0.6.7: the changelog entry, and the version in every lockfile that pins it ... 50c6f8ec95

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

dcharlot merged commit e08b05897a into main 2026-10-19 22:37:45 -04:00

dcharlot referenced this pull request from a commit 2026-10-19 22:37:47 -04:00

Merge pull request 'wai-quantum 0.6.7: tensor networks that split controlled gates and fix projections' (#343) from wai/quantum-tn-split-0.6.7 into main

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