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arxiv: 2604.07704 · v1 · submitted 2026-04-09 · 🪐 quant-ph · math-ph· math.MP

Recognition: 2 theorem links

· Lean Theorem

Trotterization with Many-body Coulomb Interactions: Convergence for General Initial Conditions and State-Dependent Improvements

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Pith reviewed 2026-05-10 18:24 UTC · model grok-4.3

classification 🪐 quant-ph math-phmath.MP
keywords TrotterizationCoulomb interactionsQuantum simulationError boundsMany-body systemsConvergence ratesQuantum computingHydrogenic atoms
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The pith

Second-order Trotter formulas for many-body Coulomb Hamiltonians achieve a sharp 1/4 convergence rate for general initial conditions with polynomial error dependence on particle number.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

This paper establishes rigorous error bounds for Trotter formulas when applied to many-body quantum systems whose Hamiltonians include Coulomb interactions. For arbitrary initial states in the domain of the Hamiltonian, the second-order Trotter method converges at a sharp rate of 1/4, with an explicit prefactor that grows only polynomially with the number of particles. This bound holds without any regularization of the singular Coulomb potential. Under additional physically motivated conditions on the initial state, such as those satisfied by high-angular-momentum excited states in hydrogenic systems, the convergence rate improves to first or second order. The findings address the challenges posed by unbounded operators and singular potentials while confirming that the approach remains efficient for quantum simulation of physically relevant cases.

Core claim

The central claim is that second-order Trotterization applied to the many-body Hamiltonian with Coulomb interactions produces an error that scales as the fourth root of the time step for any initial state in the domain of the Hamiltonian, with the prefactor depending polynomially on particle number. This holds despite the unbounded kinetic energy, the singular and long-range nature of the Coulomb potential, and the exponential growth of the Hilbert space. The paper further shows that physically natural restrictions on the initial state, linked for example to high angular momentum in hydrogenic atoms, restore higher-order convergence.

What carries the argument

The second-order Trotter formula (Suzuki-Trotter decomposition) applied to the sum of the kinetic-energy operator and the many-body Coulomb potential, together with operator-theoretic error analysis that tracks domains and commutators without assuming extra regularity.

If this is right

  • Quantum algorithms for simulating many-body Coulomb systems remain efficient on quantum hardware without introducing regularization of the singularity.
  • The 1/4-rate bound applies to broad classes of initial conditions, including the hydrogen ground state observed in earlier numerics.
  • State-dependent conditions allow first- or second-order convergence for suitable excited states in atomic systems.
  • The polynomial scaling in particle number justifies Trotterization for quantum chemistry without size-dependent overhead from regularization.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The same domain-based analysis could be tested on other singular long-range potentials appearing in quantum many-body problems.
  • Preparing initial states with high angular momentum may be a practical route to recover higher-order accuracy in simulations.
  • The explicit particle-number dependence supplies a concrete target for benchmarking quantum simulators on small Coulomb systems.
  • Absence of regularization removes one source of systematic bias when comparing simulated real-time dynamics to experimental spectra.

Load-bearing premise

The initial state must lie in the domain of the unbounded Hamiltonian and the Coulomb potential must satisfy the stated operator properties without regularization or cutoff.

What would settle it

A direct numerical computation of the Trotter error on a small-particle Coulomb system with a general initial state in the Hamiltonian domain, showing that the observed scaling with time step fails to match the predicted 1/4 rate.

read the original abstract

Efficiently simulating many-body quantum systems with Coulomb interactions is a fundamental question in quantum physics, quantum chemistry, and quantum computing, yet it presents unique challenges: the Hamiltonian is an unbounded operator (both kinetic and potential parts are unbounded); its Hilbert space dimension grows exponentially with particle number; and the Coulomb potential is singular, long-ranged, non-smooth, and unbounded, violating the regularity assumptions of many prior state-of-the-art many-body simulation analyses. In this work, we establish rigorous error bounds for Trotter formulas applied to many-body quantum systems with Coulomb interactions. Our first main result shows that for general initial conditions in the domain of the Hamiltonian, second-order Trotter achieves a sharp $1/4$ convergence rate with explicit polynomial dependence of the error prefactor on the particle number. The polynomial dependence on system size suggests that the algorithm remains quantumly efficient, even without introducing any regularization of the Coulomb singularity. Notably, although the result under general conditions constitutes a worst-case bound, this rate has been observed in prior work for the hydrogen ground state, demonstrating its relevance to physically and practically important initial conditions. Our second main result identifies a set of physically meaningful conditions on the initial state under which the convergence rate improves to first and second order. For hydrogenic systems, these conditions are connected to excited states with sufficiently high angular momentum. Our theoretical findings are consistent with prior numerical observations.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The manuscript establishes rigorous error bounds for Trotter formulas applied to many-body quantum systems with Coulomb interactions. Its first main result claims that second-order Trotter achieves a sharp 1/4 convergence rate for general initial conditions in the domain of the Hamiltonian, with an explicit error prefactor that depends polynomially on particle number N. The second main result identifies physically motivated conditions on the initial state (e.g., sufficiently high angular momentum in hydrogenic systems) under which the rate improves to first or second order. These bounds are presented without regularization of the singular Coulomb potential.

Significance. If the derivations are correct, the work is significant because it extends Trotter error analysis to unbounded operators with singular, long-range potentials that violate standard regularity assumptions. The polynomial N-dependence supports quantum efficiency for realistic many-body simulations, and the state-dependent improvements align with prior numerical observations on hydrogen ground states, providing both theoretical justification and practical guidance.

major comments (2)
  1. [Proof of first main result / Theorem on 1/4 rate] The first main result (abstract and associated theorem): the claimed 1/4 rate for arbitrary initial states in dom(H) requires explicit control of the Trotter remainder via commutator estimates between the kinetic operator T and the singular many-body Coulomb potential V. Standard proofs rely on operator-boundedness or Kato-Rellich relative boundedness, but V is only form-bounded relative to T and its derivatives introduce stronger singularities; the manuscript must supply the precise domain arguments and bounds showing that these estimates close with polynomial N-dependence, as failure here would invalidate the general-initial-condition claim.
  2. [Operator-domain arguments / assumptions on V] Section on operator properties (likely near the statement of the main theorems): the abstract asserts that the Coulomb potential satisfies the required operator properties without regularization, yet the many-body sum V = sum_{i<j} 1/|r_i - r_j| is unbounded and the domain of [T,V] is not automatically guaranteed to be dense or to yield the needed remainder bounds. Explicit verification that the error expansion remains valid for general psi in dom(H) is needed to support the polynomial prefactor.
minor comments (2)
  1. [Abstract] The abstract states that the 1/4 rate 'has been observed in prior work for the hydrogen ground state' but does not cite the specific numerical reference; adding the citation would improve traceability.
  2. [Notation and definitions] Notation for the Trotter product (e^{-itT/n} e^{-itV/n})^n should be clarified with respect to the ordering and time-step convention to avoid ambiguity in the error analysis.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their careful reading and constructive comments, which help strengthen the rigor of our proofs. We address each major comment point by point below.

read point-by-point responses
  1. Referee: [Proof of first main result / Theorem on 1/4 rate] The first main result claims that second-order Trotter achieves a sharp 1/4 convergence rate for general initial conditions in dom(H), requiring explicit control of the Trotter remainder via commutator estimates between the kinetic operator T and the singular many-body Coulomb potential V. Standard proofs rely on operator-boundedness or Kato-Rellich relative boundedness, but V is only form-bounded relative to T and its derivatives introduce stronger singularities; the manuscript must supply the precise domain arguments and bounds showing that these estimates close with polynomial N-dependence.

    Authors: We agree that the commutator estimates and domain arguments require explicit presentation to support the general-initial-condition claim. In the proof of Theorem 1, we control the Trotter remainder using the form-boundedness of the many-body Coulomb potential relative to the kinetic energy T, combined with Hardy-type inequalities that handle the singularities without regularization. The polynomial N-dependence follows from collective bounds over the O(N^2) pairwise terms. To address the concern directly, we have added a dedicated subsection in the revised Section 3 with the precise domain verifications and commutator bounds, confirming closure in dom(H) for arbitrary initial states. revision: yes

  2. Referee: [Operator-domain arguments / assumptions on V] Section on operator properties: the abstract asserts that the Coulomb potential satisfies the required operator properties without regularization, yet the many-body sum V is unbounded and the domain of [T,V] is not automatically guaranteed to be dense or to yield the needed remainder bounds. Explicit verification that the error expansion remains valid for general psi in dom(H) is needed to support the polynomial prefactor.

    Authors: We acknowledge the need for explicit verification of the operator domains. While V is unbounded, we establish in the manuscript that for psi in dom(H), the relevant commutators [T,V] are well-defined in the strong sense via the specific 3D Coulomb singularity structure, which permits relative form-boundedness. The domain is dense because C^infty_c functions are dense in dom(H) for these operators. We have expanded the operator-properties section (now including a new Lemma) with the explicit verification that the error expansion holds for general psi in dom(H) and that the prefactor remains polynomial in N, without any regularization of V. revision: yes

Circularity Check

0 steps flagged

No significant circularity; derivation is self-contained mathematical proof

full rationale

The paper derives error bounds for second-order Trotterization on many-body Coulomb Hamiltonians via direct operator-theoretic estimates, including domain considerations for unbounded operators and commutator bounds that yield the 1/4 rate with polynomial N-dependence. No steps reduce by construction to fitted inputs, self-definitions, or self-citation chains; the central claims rest on explicit lemmas for general initial states in dom(H) and state-dependent improvements, without renaming known results or smuggling ansatzes. Self-citations (if present) are not load-bearing for the new convergence statements, which are presented as independent derivations consistent with but not derived from prior numerical observations.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

The central claim rests on the initial state belonging to the domain of the Hamiltonian and on standard properties of unbounded self-adjoint operators and the Trotter product formula; no free parameters or new entities are introduced in the abstract.

axioms (2)
  • domain assumption Initial state belongs to the domain of the Hamiltonian
    Explicitly required for the general-initial-condition result.
  • standard math Trotter product formula applies to the sum of kinetic and Coulomb operators
    Background assumption from functional analysis invoked for error-bound derivation.

pith-pipeline@v0.9.0 · 5555 in / 1367 out tokens · 51632 ms · 2026-05-10T18:24:57.037330+00:00 · methodology

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Reference graph

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