Preprint of the article "A fixed-level certification dichotomy for an infinite family of frustration-free spin chains" (22 pages, no figures). To every finite loopless directed graph T the paper attaches a rational, range-three, frustration-free spin-chain interaction: arcs of T carry hopping bands for domain walls, missing arcs act as hard local penalties. The main theorem is the exact three-term equivalence: T is acyclic <=> liminf_m gap_m(T) > 0 <=> delta_LTI(5) > 0, where gap_m is the spectral gap of the periodic chain on m sites and delta_LTI(5) is the value of the local translation-invariant (LTI) semidefinite certification hierarchy at level 5, its first sound level. The certification level is fixed while the size of the graph and the local Hilbert-space dimension are unbounded across the family. To the author's knowledge, this is the first fixed-level completeness result for a spectral-gap certification hierarchy over an infinite family of frustration-free chains: a single finite combinatorial invariant, acyclicity, decides both the thermodynamic spectral gap and the success of the certificate at one universal level. The acyclic direction is proved by an explicit rational certificate, a superpotential built from a topological height and three local corrections, giving delta_LTI(5) >= min{1/48, 1/sqrt(12H)} for a DAG of height H. The cyclic direction is made quantitative by a free-fermion analysis of the invariant winding sectors: directed cycles carry a diffusive lowest mode of energy of order 1/m^2, and the finite-volume gaps of the directed 2- and 3-cycles are computed exactly, 2(1-cos(pi/m)) and 2(1-cos(2pi/m)). The relationship with the PVBS chains of Bachmann and Nachtergaele and with earlier gapped-gapless classifications is discussed explicitly. All computer-assisted statements use exact symbolic arithmetic. The complete reproducibility package (symbolic pipeline, generated blocks with exact characteristic polynomials, Sturm data, LDL^T certificates, SHA-256 digests) is archived separately at https://doi.org/10.5281/zenodo.21790411. The manuscript has been submitted to Reports on Mathematical Physics.
Preprint of the article "A fixed-level certification dichotomy for an infinite family of frustration-free spin chains" (22 pages, no figures). To every finite loopless directed graph T the paper attaches a rational, range-three, frustration-free spin-chain interaction: arcs of T carry hopping bands for domain walls, missing arcs act as hard local penalties. The main theorem is the exact three-term equivalence: T is acyclic <=> liminf_m gap_m(T) > 0 <=> delta_LTI(5) > 0, where gap_m is the spectral gap of the periodic chain on m sites and delta_LTI(5) is the value of the local translation-invariant (LTI) semidefinite certification hierarchy at level 5, its first sound level. The certification level is fixed while the size of the graph and the local Hilbert-space dimension are unbounded across the family. To the author's knowledge, this is the first fixed-level completeness result for a spectral-gap certification hierarchy over an infinite family of frustration-free chains: a single finite combinatorial invariant, acyclicity, decides both the thermodynamic spectral gap and the success of the certificate at one universal level. The acyclic direction is proved by an explicit rational certificate, a superpotential built from a topological height and three local corrections, giving delta_LTI(5) >= min{1/48, 1/sqrt(12H)} for a DAG of height H. The cyclic direction is made quantitative by a free-fermion analysis of the invariant winding sectors: directed cycles carry a diffusive lowest mode of energy of order 1/m^2, and the finite-volume gaps of the directed 2- and 3-cycles are computed exactly, 2(1-cos(pi/m)) and 2(1-cos(2pi/m)). The relationship with the PVBS chains of Bachmann and Nachtergaele and with earlier gapped-gapless classifications is discussed explicitly. All computer-assisted statements use exact symbolic arithmetic. The complete reproducibility package (symbolic pipeline, generated blocks with exact characteristic polynomials, Sturm data, LDL^T certificates, SHA-256 digests) is archived separately at https://doi.org/10.5281/zenodo.21790411. The manuscript has been submitted to Reports on Mathematical Physics.
Estimating spectral gaps of quantum many-body Hamiltonians is a highly challenging computational task, even under assumptions of locality and translation-invariance. Yet, the quest for rigorous gap certificates is motivated by their broad applicability, ranging from many-body physics to quantum computing and classical sampling techniques. Here we present a general method for obtaining lower bounds on the spectral gap of frustration-free quantum Hamiltonians in the thermodynamic limit. We formulate the gap certification problem as a hierarchy of optimization problems (semidefinite programs) in which the certificate – a proof of a lower bound on the gap – is improved with increasing levels. Our approach encompasses existing finite-size methods, such as Knabe's bound and its subsequent improvements, as those appear as particular possible solutions in our optimization, which is thus guaranteed to either match or surpass them. We demonstrate the power of the method on one-dimensional spin-chain models where we observe an improvement by several orders of magnitude over existing finite size criteria in both the accuracy of the lower bound on the gap, as well as the range of parameters in which a gap is detected.
This record contains the preprint and the complete reproducibility package for “A formal finite-size spectral-map hierarchy for free-fermion entanglement”. The work studies the finite-size deformation of the spectral relation between the discrete prolate (Slepian) eigenvalue and the one-particle entanglement energy in a critical free-fermion chain. Using the exact DPSWF representation, Riccati/Dunham analysis and finite-part period calculus, an all-orders formal hierarchy is derived in which the finite-size coefficients satisfyFj=Pj(D)Φ∞F_j=P_j(D)\Phi_\infty, with PjP_j a rational function of the Euler operator D=t∂tD=t\partial_t. The work establishes universal denominator, degree and zero structures for these rational operators, including additional even-shift factors, and derives their Weber/Bernoulli leading behaviour. Independent checks include exact reconstruction of the half-filling Fisher–Hartwig phase polynomials Q20,Q40,Q60,Q80Q_{20},Q_{40},Q_{60},Q_{80}, exact Legendre reduction at the spectral centre, rational operator reconstruction through j=13j=13, and finite-matrix validation of the first two finite-size coefficients. The archive accompanying the manuscript contains the scripts, exact symbolic calculations, numerical data, regression tests and SHA-256 manifests required to reproduce the principal computational claims. The manuscript explicitly distinguishes the proved formal Dunham hierarchy from the still-open uniform physical connection/remainder theorem.
This research establishes an exact, matrix-free framework for spectral analysis of Fibonacci-constrained quantum systems, demonstrating how exponentially expanding Hilbert spaces can admit computational descriptions whose complexity grows only linearly with chain length at any fixed spectral moment order. The investigation focuses on the open PXP quantum chain, whose admissible configurations obey a nearest-neighbor exclusion constraint and form a Hilbert space of dimension dim(Hₙ) = Fₙ₊₂. By combining Fibonacci combinatorics, Zeckendorf indexing, temporal-mask transfer operators, and exact integer arithmetic, the study develops a unified mathematical approach to spectral moments, constrained quantum dynamics, and gauge-sensitive observables without explicitly constructing the exponentially large Hamiltonian matrix. The central result is a universal rational hierarchy of even spectral moments, expressed through the generating function Σₙ₌₀∞ Tr(Aₙ²ᵐ) zⁿ = Pₘ(z) / (1 − z − z²)ᵐ⁺¹, with deg Pₘ ≤ 3m + 2. This theorem establishes that every fixed-order even spectral moment possesses a rational generating function governed by a power of the Fibonacci characteristic polynomial. Consequently, infinitely many spectral moments across increasing chain lengths can be reconstructed from a finite collection of exact initial values. Explicit rational expressions are derived for the fourth, sixth, and eighth spectral moments, accompanied by integer recurrence relations and independently reproducible computational certificates. The underlying temporal-mask transfer identity reduces fixed-order moment evaluation to O(n) arithmetic operations, even with spatially inhomogeneous hopping amplitudes and local diagonal fields. Its computational constants depend exponentially on moment order, but not on the exponentially growing Hilbert-space dimension. A complementary result introduces an exact gauge-sensitive fourth-moment certificate for quantum chains carrying occupation-dependent hopping phases. The spectral response obeys the identity Tr(Hₙ,φ⁴) − Tr(Hₙ,₀⁴) = 8(cos φ − 1) Sₙ, where Sₙ is obtained through a Fibonacci-based weighted recurrence requiring only O(n) arithmetic operations. Remarkably, this identity remains valid under arbitrary static real diagonal disorder, provided the diagonal energies and hopping magnitudes remain unchanged between phase settings. It therefore isolates a precisely defined gauge-dependent contribution to the fourth spectral moment without requiring diagonalization or knowledge of the complete spectrum. The certificate reconstructs a dimensionless flux response rather than an absolute quantum-action scale. The broader significance lies in demonstrating that exponential state-space growth does not necessarily imply exponential computational complexity for every exact spectral observable. The results connect constrained quantum many-body physics, Fibonacci graph theory, rational generating functions, and finite-state transfer methods within a common algebraic framework. All reported coefficients are supported by exact-integer verification rather than numerical fitting, and the established complexity bounds concern arithmetic operations rather than total bit complexity. The work provides a reproducible mathematical foundation for further investigations of spectral invariants, gauge responses, quantum constraints, and scalable symbolic computation, while restricting its formal claims to the specified finite-dimensional Hamiltonian models. Keywords: Fibonacci-constrained quantum chains · PXP Hamiltonian · Rational spectral hierarchy · Matrix-free computation · Temporal-mask transfer · Zeckendorf indexing · Gauge invariants · Exact spectral moments · Quantum many-body systems · Integer verification
This record contains the full author preprint (12 pages), its mathematical supplement (17 pages), and the complete article archive with LaTeX sources, the version note, SHA-256 manifests and the licence. The two PDFs are also provided as individual files for direct reading. Version v3 clarifies the Haar normalization convention in section 9.1 of the mathematical supplement (equation 45). The unnormalised transform H has H*H = 2I and Tr(HQH*) = 2Tr(Q); the equivalent orthogonal transform is H/sqrt(2). This agrees with the existing root/detail identity and exact verifier. The main article, verification code, Lean files, matrix certificates and stated constants are unchanged. See the publication version note for the precise scope of this correction. AbstractWe prove that the nearest-neighbor spin-1/2 antiferromagnetic Heisenberg model on the infinite Kagome lattice is gapless in the bulk GNS sense. The argument constructs six explicit local preimages and their complete infinite-lattice Hamiltonian commutators. Two rigorous 17-spin positivity certificates, each decomposed into 31 nontrivial swap-character blocks and nine SU(2) multiplicity blocks, give a state-uniform off-kernel mass floor. Exact operator transport on the two genuine outward Kagome continuations propagates the same physical family through a finite stationary interface. A root/detail/current decomposition, a local current–boundary identity, and state-uniform norm estimates yield a horizon-independent Dirichlet-energy bound. With harmonic weights, for every infinite-volume ground state ω and every R ≥ 1 the same finite family satisfies M_R(ω) ≥ (15/32) ∑_{k=1}^{R} 1/k and E_R(ω) ≤ 761429817528146602401/25088000. Any positive GNS gap would force the second quantity to diverge with the first. Hence every admissible ground-state representation has zero gap, and the declared bulk gap is zero. All finite operator identities and matrix inequalities are checked from exact algebraic data, with rigorous ball arithmetic used for the large positive-definiteness tests. Lean 4 verifies the arbitrary-horizon harmonic implication and the final variational contradiction. The proof uses neither finite-size gap extrapolation nor a spectral cutoff. Companion public verification code, Lean 4 formalization and exact certificates: https://doi.org/10.5281/zenodo.23675708 Distribution and reuse are governed by the Public Scientific Evaluation and Reproducibility Terms included with this record. The deposit excludes the author's private discovery engine and proprietary know-how.
Here is the finding. For frustration-free spin-1/2 chains, the spectral gap question is decidable. We can completely classify these systems into gapped and gapless phases. This holds even though the general problem for translationally invariant Hamiltonians is undecidable, as shown by Cubitt, Perez-Garcia, and Wolf in 2015. Here is the context. We are talking about Hamiltonians written as a sum of local terms, each positive semidefinite, with a ground state annihilated by every term. That is the frustration-free condition. The spectral gap is the energy difference between the first excited state and the ground state. For a general quantum many-body system, determining whether that gap closes in the thermodynamic limit is notoriously hard. But for this restricted class, the mathematics gives us a clean answer. Here is the mechanism. The key is the matrix product state representation. The ground state of a gapped phase has finite correlation length. Its MPS transfer matrix is injective Author: Andrew Stewart Caldin, Independent Researcher, UK. Part of the E8 Intelligence Research series. Platform: e8intelligence.com
We study the descriptive complexity of the relation that two finite-range translation-invariant quantum spin interactions belong to the same gapped phase. The key observation is that this relation is exactly an increasing union of arc-connection relations of closed uniformly gapped sets, bringing the classification problem into classical continuum topology. On the Polish space of finite-range interactions, the gapped set is Borel of rank at most four under standard definitions of the spectral gap, and the gap functional is upper semicontinuous with attained supremum. On the uniformly gap-stable interior, the phase relation is smooth: its classes are the countably many open connected components, with a locally constant complete invariant. Standard frustration-free models satisfying local topological quantum order lie in this interior, so any descriptive complexity is confined to the unstable boundary. Homogeneity of the gap yields a radial reduction for finite-dimensional coupling families. Consequently, two-coupling families have a smooth phase relation; for three couplings, every fixed-gap-level relation is Borel reducible to the eventual-equality relation E0, and the full phase relation is Borel and therefore not Σ11-complete; four independent interaction directions are the first dimension in which general analytic arc-connection complexity is no longer topologically excluded. Finite levels of the defining gap constraints are semialgebraic.