Kossakowski-form dissipator + dissipative pc_step_orbit_rep validation by AlexSchuckert · Pull Request #179 · QuEraComputing/ppvm

AlexSchuckert · 2026-07-16T11:50:28Z

Stacked on #178 (base: continuous-time-pauli-propagation).

What this adds

Kossakowski-form dissipators: D*(O) = Σ_nm K_nm (A_n† O A_m − ½{A_n†A_m, O}) specified directly by an operator list + Hermitian PSD pair matrix — the natural form for collective decay (every emitter pair shares a channel via Γ_nm from the free-space Green's function). Mathematically identical to eigendecomposing K into N dense collective jumps, but the per-string action costs one term-pair product per nonzero K_nm instead of carrying an extra factor of N: O(N²) instead of O(N³).

Rust: one JumpKind::KossakowskiPair per nonzero K_nm (precompiled sandwich table + A_n†A_m lincomb, per-pair support masks), plugged into compute_action_terms — so action/leakage/generator/pc_step/pc_step_orbit_rep all inherit it. Includes a one-sided fast path: strings touching only one of a pair's two sites collapse to ±½[K·A_n†A_m, p] (4 Pauli products instead of 12; the dominant case for local strings under dense K).
Python: Lindbladian(..., kossakowski=(ops, K)), validating Hermiticity and positive semidefiniteness (raises — no silent clipping). Coexists with jump_terms.

Dissipative pc_step_orbit_rep validation: the orbit path applies jump/Kossakowski terms correctly with no code change. Under the 1/|G| projection convention of canonicalize_basis_arr_complex (c_rep = coeff_word/|Stab|), the phase-aware action is exact for any translation-equivariant generator, including transitions between orbits of different sizes (the non-unital Z→I flow). Corollary (documented + tested): a translation-invariant {I,Z} observable reads out as |G|·Σ c_rep.

Numbers

Measured per-pc_step wall (criterion, B=4096, superradiance chain d=0.1λ₀), eigenmode jumps vs Kossakowski:

N	eigenmode	Kossakowski	win
10	274 ms	81 ms	3.4×
20	1.43 s	161 ms	8.9×
30	4.35 s	250 ms	17.4×

(pre-optimization Kossakowski walls; two further kept optimizations take another ~40% off — full history in docs/autotune/2026-07-16-kossakowski/).

Validation

Representation equivalence: random models (mixed σ⁻ + generic lincomb ops, real and complex Hermitian PSD K) ≤ 1e-12; N=6 superradiance chain vs eigenmode ≤ 1e-11.
Physics: N=6 chain R(t) vs exact excitation-cascade ED < 1e-4 (vs the stored fig11 exact reference: 1.1e-05).
Orbit path: N=6 ring orbit-vs-projected-full equivalence ~2e-15 (both representations); R(t) vs ring ED < 1e-4; N=10 truncated-regime sanity (finite, admission-bounded, monotone in rep budget); identity bookkeeping vs closed form ≤ 1e-9.
Leakage coverage test guarantees admission sees Kossakowski terms.
250 Python tests + Rust suites green; coherent regression gates bit-identical; zero clippy warnings.

🤖 Generated with Claude Code

github-actions · 2026-07-16T12:07:32Z

PR Preview Action v1.8.1
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2026-09-02 07:20 UTC

…daptive Lindbladian evolution Direct Heisenberg-picture evolution O ← exp(dt·L*)O on an adaptively truncated Pauli-string basis: exact in dt within the working basis, no Trotter splitting. LindbladSpec precompiles Hermitian-Pauli (fast diagonal) and general complex Pauli-sum jumps (σ±, amplitude damping, precomputed L†L); pc_step does two-hop leakage enrichment + predictor/ corrector matrix-free exponential via quspin-expm (MIT), with the truncation policy in one PcStepConfig (max_basis rank cap, admit_basis displacement bound, drop_tol prune, tau_add admission filter). Python: ppvm.Lindbladian with numpy hot path + string convenience API, mimalloc global allocator (~50% peak-RSS cut on adaptive paths), two jupytext demos, tests against dense-Liouvillian / closed-form / eig references. Split 2/4 of the CTPP work; the momentum-sector (orbit-rep) evolution follows in split 3. Full history: branch continuous-time-pauli-propagation. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Two consumers of the translation-symmetry primitive: Trotter path: PauliSum.symmetry_merge (k=0) and PauliSum.momentum_merge (k≠0 carried as a real pair, character-weighted fold, |G|-rescaled to the summing projector so merging after every step is idempotent), with TranslationGroup and canonicalize_basis_arr{,_complex} / check_momentum_sector_arr exposed to Python. Inputs validated at the boundary (ValueError, not panics). CTPP path: pc_step_orbit_rep — per-step evolution entirely in orbit-representative form (complex coefficients, phase-aware action, cached-CSC expm; basis ~|G|× smaller than full-basis evolution, persisting through every step), with the same PcStepConfig truncation policy incl. displacement admission. Split 3/4 of the CTPP work; full history on branch continuous-time-pauli-propagation. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

The complete experiment ledgers behind the CTPP design decisions: truncation-scheme comparisons (cap/valve vs displacement vs thresholds), the momentum-vs-real-space study, exact-reference methodology, the L=21/L=41 application exhibits, and every kept or discarded attempt with its measured numbers. Scan drivers and ED reference generators included as text; plots and .npz exact-reference data (~2.5 MB) live on the archive branch continuous-time-pauli-propagation. Split 4/4 of the CTPP work. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

…rep validation D*(O) = Σ_nm K_nm (A_n†OA_m − ½{A_n†A_m,O}) from an operator list + Hermitian PSD pair matrix — exactly equivalent to the eigenmode-jump representation but O(N²) instead of O(N³) per string (measured 3.4×/8.9×/17.4× per pc_step at N=10/20/30 on the superradiance chain; criterion bench included). One JumpKind::KossakowskiPair per nonzero K_nm with a precompiled sandwich table and a one-sided ±½[K·A_n†A_m, p] commutator fast path; all step/leakage/generator paths inherit it via compute_action_terms. Python: Lindbladian(..., kossakowski=(ops, K)) with Hermiticity/PSD validation (raises, no silent clipping). Dissipative pc_step_orbit_rep validated correct out of the box (the 1/|G| projection convention makes the phase-aware action exact for any equivariant generator, incl. the non-unital Z→I flow): orbit vs projected-full ≤1e-12, R(t) vs excitation-cascade ED <1e-4, identity bookkeeping vs closed form, truncated-regime sanity. Physics regression: N=6 superradiance chain vs exact cascade <1e-4 (vs the fig11 stored reference: 1.1e-05). Squashed from archive/kossakowski-dissipator (full history there). Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>