wai-quantum 0.3.34: ground states of spin chains by DMRG, held to exact answers #159

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dcharlot merged 1 commit from wai-quantum-dmrg into main 2026-10-05 12:53:37 -04:00

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dcharlot commented 2026-10-05 09:50:45 -04:00

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Stacked on #156 (→ #155 → #151). Merge those first; this diff then reduces to the one commit.

What

quantum_dmrg (wai-quantum 0.3.34) finds ground states of 1D spin chains by two-site DMRG and holds the results to exact answers.

• Chains. Nearest-neighbour spin-½ chains with real terms (XXZ Heisenberg in a field, transverse-field Ising), written as matrix-product operators.
• The solver.
  • Each two-site step finds the lowest state by Lanczos with full re-orthogonalisation.
  • It truncates using the eigenvectors of the reduced density matrix, with a maximum bond and a weight cutoff.
  • It reports the discarded weight and the entanglement entropy at every bond.
• An in-crate symmetric eigensolver (tred2/tql2).
• Exact referees.
  • Full diagonalisation, up to 22 sites.
  • The open transverse-field Ising chain solved as free fermions, at any length.
• Threads. The heaviest step, applying the two-site Hamiltonian, is split by rows across threads. The result is bit-identical at any thread count.
• CLI. wai-quantum dmrg …. Example: dmrg_chain.

Checked

• Eigensolver. It reconstructs random symmetric matrices to 1e-12.
• Free-fermion formula. It equals exact diagonalisation for n = 4, 7 and 10 at three couplings.
• DMRG against exact diagonalisation. Energies agree to 1e-8 on Heisenberg and Ising chains of 10–12 sites.
• Critical Ising chain. Error per site against the exact energy: 1.1e-11 at 100 sites, 1.4e-11 at 200 sites.
• Heisenberg chain, 100 sites. Converges from above: −44.127739250 at bond 64, −44.127739889 at bond 128.
• Behaviour. Variational, monotone across sweeps, repeatable.
• Threading. A direct test of the threaded two-site Hamiltonian fails on a 1e-15 change to one block of rows.
• Pointer-width bug found and fixed. The cross-platform pin showed the exact-diagonalisation start vector differed on wasm32: it multiplied in usize, which wraps differently there. It now uses u64. All 19 pins hold natively and under wasm32-wasip2, and CLI output is byte-identical between the two.
• Speed. Profiling led to two changes: a configurable Lanczos tolerance (default 1e-8) and threading the effective Hamiltonian. Together they took the 100-site Heisenberg run at bond 128 from 680 s to 162 s.
• Lint and tests. Clippy is clean; the eigensolver keeps its published index-loop form under an explicit allow. The prose checks pass. The new tests take 18 s in debug, and all 421 library tests pass.

🤖 Generated with Claude Code

Stacked on #156 (→ #155 → #151). Merge those first; this diff then reduces to the one commit. ## What `quantum_dmrg` (wai-quantum 0.3.34) finds ground states of 1D spin chains by two-site DMRG and holds the results to exact answers. - **Chains.** Nearest-neighbour spin-½ chains with real terms (XXZ Heisenberg in a field, transverse-field Ising), written as matrix-product operators. - **The solver.** - Each two-site step finds the lowest state by Lanczos with full re-orthogonalisation. - It truncates using the eigenvectors of the reduced density matrix, with a maximum bond and a weight cutoff. - It reports the discarded weight and the entanglement entropy at every bond. - **An in-crate symmetric eigensolver** (tred2/tql2). - **Exact referees.** - Full diagonalisation, up to 22 sites. - The open transverse-field Ising chain solved as free fermions, at any length. - **Threads.** The heaviest step, applying the two-site Hamiltonian, is split by rows across threads. The result is bit-identical at any thread count. - **CLI.** `wai-quantum dmrg …`. Example: `dmrg_chain`. ## Checked - **Eigensolver.** It reconstructs random symmetric matrices to 1e-12. - **Free-fermion formula.** It equals exact diagonalisation for n = 4, 7 and 10 at three couplings. - **DMRG against exact diagonalisation.** Energies agree to 1e-8 on Heisenberg and Ising chains of 10–12 sites. - **Critical Ising chain.** Error per site against the exact energy: 1.1e-11 at 100 sites, 1.4e-11 at 200 sites. - **Heisenberg chain, 100 sites.** Converges from above: −44.127739250 at bond 64, −44.127739889 at bond 128. - **Behaviour.** Variational, monotone across sweeps, repeatable. - **Threading.** A direct test of the threaded two-site Hamiltonian fails on a 1e-15 change to one block of rows. - **Pointer-width bug found and fixed.** The cross-platform pin showed the exact-diagonalisation start vector differed on wasm32: it multiplied in `usize`, which wraps differently there. It now uses `u64`. All 19 pins hold natively and under wasm32-wasip2, and CLI output is byte-identical between the two. - **Speed.** Profiling led to two changes: a configurable Lanczos tolerance (default 1e-8) and threading the effective Hamiltonian. Together they took the 100-site Heisenberg run at bond 128 from 680 s to 162 s. - **Lint and tests.** Clippy is clean; the eigensolver keeps its published index-loop form under an explicit allow. The prose checks pass. The new tests take 18 s in debug, and all 421 library tests pass. 🤖 Generated with [Claude Code](https://claude.com/claude-code)

dcharlot added 6 commits 2026-10-05 09:50:46 -04:00

wai-quantum 0.3.31: quantum-inspired optimisation, a re-runnable classical baseline ... 92f9e000cd

Optimisation is the claim made most often for quantum hardware, and each such
claim is a comparison with a classical solver. quantum_qio is that solver,
deterministic and re-checkable:

- Ising problems (sparse symmetric J, fields h) and Max-Cut (J = -w), a G-set
  reader, and the +-1 all-to-all spin glass.
- Simulated bifurcation from its published update rules: symplectic Euler,
  perfectly inelastic walls, ballistic (f = Jx) and discrete (f = J sgn x)
  forces, and both heated (arXiv:2203.08361), with c0 = c1 / (rms(J) sqrt N).
  Fields ride on an extra spin fixed at +1.
- Eight trials advance per pass over the couplings; each trial's arithmetic is
  unchanged, so a batched run leaves the same final positions bit for bit as
  one trial at a time. The test fails on a 1e-15 change to one lane.
- Simulated annealing (single-spin Metropolis, linear beta), single-flip
  descent, an exact Gray-code referee up to 34 spins (threaded), and
  step-to-solution S = N_s ln 0.01 / ln(1 - P).

Checked:
- every variant and annealing reach the exact ground state on 20-spin glasses;
- G-set best-known cuts reached (seed 1): G1 11624 (39% of 2,000-step
  trials), G2 11620, G3 11622, G11 564, G14 3064 (annealing; bifurcation
  stops at 3062), G22 13359, G43 6660; G55 reaches 10292 of 10299;
- the published dense-glass step (1.1) is unstable on sparse Max-Cut graphs:
  the stiffest mode has w^2 = a0(a0 - c0 mu_min) and mu_min = -degree, so G1's
  limit is near 0.88; documented, with the settings that work.

CLI: wai-quantum qio (--gset FILE | --sk N) --method dsb|bsb|hdsb|hbsb|sa|exact
[--descend --target --spins --json]. Example: qio_gset. Pinned bit for bit
natively and under wasm32-wasip2 (16 pins); CLI output byte-identical across
the two, threaded or not, G-set files included.

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

wai-quantum 0.3.32: union-find decoding in near-linear time ... e76acbe9e5

A fault-tolerant machine must decode each syndrome round before the next
arrives. Exact matching (quantum_match) is the accuracy reference; quantum_uf
is the fast decoder over the same matching graph:

- Grow: every fired detector starts a cluster; odd clusters (not on the
  boundary) grow all frontier edges at once, on the graph's integer weights,
  an edge between two growing clusters at double speed.
- Merge: a filled edge joins its clusters; a cluster on the boundary stops.
- Peel: each cluster's filled edges as a spanning tree, rooted at the
  boundary when it holds it, peeled leaves-first into a correction.
- Growth is event-driven: each frontier edge carries a fill time, and a merge
  reschedules only the frontier of a side whose growth changed. Fill times
  never run backwards, so events sit in a radix heap at amortised O(1).
  Profiling put 45% of the time in a binary heap before; the radix heap
  halved the time per shot at d = 21. Time now grows linearly with fired
  detectors, about 1.1-1.5 us each from d = 9 to d = 21.
- A reusable workspace resets in time proportional to the last shot.

Checked:
- every single edge of d = 3 and d = 5 graphs is corrected exactly;
- the event-driven schedule agrees with a round-by-round one (kept in the
  tests) on 2,000 shots at each of three distances, up to tie order;
- on the same 20,000 shots, union-find fails 0.92-1.18x as often as exact
  matching (d = 3-9, p = 0.003-0.007), 77x faster at d = 11; its threshold sits
  a little lower (at p = 0.007 its failures stop falling with distance).

CLI: wai-quantum qec --decoder uf|exact. Example: uf_bench. Pinned bit for bit
natively and under wasm32-wasip2 (17 pins); CLI output byte-identical.

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

wai-quantum 0.3.33: noisy circuits, and where the digital error model is off ... 0d0211af6e

Every quantum-advantage experiment reports a fidelity measured on noisy
hardware. For random-circuit sampling that is a cross-entropy (XEB) estimate,
read against a digital error model: the product of every gate's and
readout's success probability. quantum_noisy checks that arithmetic:

- Trajectories on the state vector: after each gate, one branch of each noise
  channel on the qubits it touched. Pauli channels (depolarizing, dephasing)
  stay unitary; amplitude damping jumps with probability gamma P(1) and is
  renormalised; readout flips each measured bit. Seeded per trajectory and
  reduced in order, so a run is the same bits at any thread count.
- The exact density matrix up to 12 qubits, held as a state on 2n qubits
  (U (x) U* for a gate, the Kraus sum for a channel), on the same kernels.
- linear_xeb (sampled, with a standard error), exact_xeb (the infinite-sample
  value), ideal_xeb (the circuit's own, 1 when fully scrambling) and
  digital_fidelity.

Checked:
- 4,000 trajectories land within four standard errors of the exact
  expectations, every channel on; sampled bitstrings follow the exact
  distribution with readout flips; sampled XEB converges to the exact value.
- The digital model understates the exact (normalised) XEB of 8-qubit
  brickwork circuits by 3.5-4.5% at two-qubit error 0.005 and 7-10% at 0.01,
  and the margin does not grow over 4 to 48 layers: a fixed set of errors
  near the measurement that the model counts as fatal, not a per-gate bias.
  On a circuit that does not scramble the gap is wider (0.71 vs 0.60).

CLI: wai-quantum noisy --file CIRCUIT.jsonl [noise] [--expect] [--xeb]
[--exact] [--json]. Pinned bit for bit natively and under wasm32-wasip2 (18
pins); CLI output byte-identical, threaded or not.

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

wai-quantum 0.3.32: close the optimisation pin's test function ... 79dd50d20b

The restack onto 0.3.31 left tests/bit_identity.rs with an unclosed function,
so the integration tests did not compile (the linux energy-receipts job). The
fix was staged after the commit by mistake. Also trims the union-find vs exact
matching comparison to 6,000 shots per distance (about 25 s in debug).

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

Merge branch 'wai-quantum-uf' into wai-quantum-noisy 7211402746

wai-quantum 0.3.34: ground states of spin chains by DMRG, held to exact answers ... aa64bcf112

Claims that classical computers cannot simulate a material are claims about
entanglement; in one dimension the density-matrix renormalization group
usually can, with an error it reports. quantum_dmrg:

- Chain: nearest-neighbour spin-1/2 chains with real terms (XXZ Heisenberg in
  a field, transverse-field Ising), written as matrix-product operators (the
  finite-state machine of their terms).
- Two-site DMRG: Lanczos with full re-orthogonalisation for the lowest state
  of the effective Hamiltonian; truncation by the reduced density matrix's
  eigenvectors (max bond, weight cutoff); discarded weight and the
  entanglement entropy at every bond.
- symmetric_eigen: Householder tridiagonalisation and implicit QL
  (tred2/tql2), hypotenuses in-crate.
- Exact referees: Lanczos on the full 2^n space (to 22 sites), and the open
  transverse-field Ising chain as free fermions at any length
  (E0 = -1/2 sum Lambda_k, Lambda_k^2 the eigenvalues of (A-B)(A+B)).
- The effective Hamiltonian runs in blocks of rows across threads, each row in
  the same order: bit-identical at any thread count (a direct test fails on a
  1e-15 change to one block). The Lanczos tolerance is a setting (1e-8 by
  default; the energy error goes as its square).

Checked:
- the eigensolver reconstructs random symmetric matrices to 1e-12;
- the free-fermion energy equals exact diagonalisation (n = 4, 7, 10);
- DMRG equals exact diagonalisation to 1e-8 on Heisenberg and Ising chains;
- critical Ising: 1.1e-11 per site at 100 sites, 1.4e-11 at 200 against the
  exact energy; Heisenberg 100 sites: -44.127739250 at bond 64 and
  -44.127739889 at bond 128, converging from above;
- variational, monotone in sweeps, repeatable.

The cross-platform pin caught a pointer-width bug: the exact-diagonalisation
start vector multiplied in usize, which wraps differently on wasm32; it now
uses u64, and all 19 pins hold natively and under wasm32-wasip2.

CLI: wai-quantum dmrg [--chain ising|heisenberg] [-n] [--j --jz --h] [--bond]
[--sweeps] [--exact] [--json]. Example: dmrg_chain. CLI output byte-identical
natively and under WASI.

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

dcharlot referenced this pull request 2026-10-05 11:14:04 -04:00

wai-quantum 0.3.35: time evolution of spin chains by TDVP, held to exact answers #160

dcharlot merged commit e2e039312f into main 2026-10-05 12:53:37 -04:00

dcharlot referenced this pull request from a commit 2026-10-05 12:53:38 -04:00

Merge pull request 'wai-quantum 0.3.34: ground states of spin chains by DMRG, held to exact answers' (#159) from wai-quantum-dmrg into main

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