pith. sign in

arxiv: 2605.20065 · v1 · pith:DWX2RHUInew · submitted 2026-05-19 · ❄️ cond-mat.stat-mech · cond-mat.quant-gas· quant-ph

Non-equilibrium quantum dynamics of interacting integrable models by Monte Carlo sampling Lehmann representations

Pith reviewed 2026-05-20 03:47 UTC · model grok-4.3

classification ❄️ cond-mat.stat-mech cond-mat.quant-gasquant-ph
keywords Monte Carlo samplingLehmann representationquantum quenchesintegrable modelsLieb-Liniger modelnon-equilibrium dynamicsQuench Actionorder parameter
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0 comments X

The pith

A Monte Carlo sampling scheme evaluates the Lehmann representation to compute time-dependent local observables after quantum quenches in integrable models.

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

The paper introduces a Monte Carlo sampling method to numerically evaluate the Lehmann representation for time-dependent expectation values of local operators in interacting integrable quantum systems following homogeneous quenches. This technique supports both the full Lehmann sum and the Quench Action formalism while reaching system sizes and evolution times beyond the limits of prior approaches. Benchmarks confirm agreement with exact results in non-interacting lattice and continuum models as well as short-time weak-interaction cases. The method is then used to follow the order-parameter dynamics in the repulsive Lieb-Liniger gas quenched from a Bose-Einstein condensate across a wide range of interaction strengths. The authors also identify the onset of a sign problem when the same sampling is applied to more general dynamical correlators.

Core claim

We present a Monte Carlo sampling scheme that numerically evaluates the Lehmann representation for time-dependent expectation values of local operators, allowing us to access system sizes and times significantly beyond the reach of existing methods. The approach accommodates both the full Lehmann sum and the Quench Action formalism. We benchmark against exact results for non-interacting lattice and continuum models and short-time results at weak interactions, finding excellent agreement. We apply the method to quantum quenches from a Bose-Einstein condensate in the repulsive Lieb-Liniger model and determine the time evolution of the order parameter for a wide range of interaction strengths.

What carries the argument

Monte Carlo sampling of the Lehmann sum (or Quench Action) applied to local observables

If this is right

  • The method extends the reachable scales for computing local operator dynamics after quenches in integrable models.
  • It yields the order-parameter time evolution in the Lieb-Liniger gas for arbitrary interaction strengths.
  • It identifies regimes where a sign problem appears for broader classes of dynamical correlators.
  • The same sampling framework can be applied to both full Lehmann sums and Quench Action calculations.

Where Pith is reading between the lines

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

  • The technique could be used to test predictions for relaxation toward generalized Gibbs ensembles in systems too large for exact diagonalization.
  • Similar sampling ideas might be adapted to track local observables in quenches that break integrability weakly.
  • Efficiency gains could allow systematic studies of finite-size effects on prethermalization plateaus.

Load-bearing premise

The Monte Carlo sampling of the Lehmann sum remains efficient and sign-problem free for the local observables and interaction regimes studied.

What would settle it

Numerical evidence that the Monte Carlo estimator variance grows exponentially with system size or time for local operators in the Lieb-Liniger model at moderate interactions would falsify the claimed efficiency and scalability.

Figures

Figures reproduced from arXiv: 2605.20065 by Fabian H. L. Essler, Riccardo Senese.

Figure 1
Figure 1. Figure 1: FIG. 1. Comparison of [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2. MC results from QA ( [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: are well fitted by (see SM) ⟨ϕ(x, t)⟩ ∝ e −iω(c,n)t e −t/τ(c,n) . (12) The frequency ω(c, n) > 0 and decay time τ (c, n) > 0 are expected to have a non-trivial analytical dependence on c and n, cf. the case of ⟨σ x j (t)⟩ in TFIC from Ref. [75]. The MC method provides very useful information on the structure of the spectral sum [41]. As in interacting the￾ories the relevant |F{λ(j)} | are exponentially sma… view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4. Dots show QA and DS spectral weights ( [PITH_FULL_IMAGE:figures/full_fig_p004_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: FIG. 5. Log-scale plots showing convergence with [PITH_FULL_IMAGE:figures/full_fig_p007_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: FIG. 6. Log-log plots showing the decay with [PITH_FULL_IMAGE:figures/full_fig_p007_6.png] view at source ↗
read the original abstract

Determining the dynamics of interacting integrable many-particle quantum systems at finite times after homogeneous quantum quenches is a long-standing challenge. We present a Monte Carlo sampling scheme that numerically evaluates the Lehmann representation for time-dependent expectation values of local operators, allowing us to access system sizes and times significantly beyond the reach of existing methods. The approach accommodates both the full Lehmann sum and the Quench Action formalism. We benchmark against exact results for non-interacting lattice and continuum models and short-time results at weak interactions, finding excellent agreement. We apply the method to quantum quenches from a Bose-Einstein condensate in the repulsive Lieb-Liniger model and determine the time evolution of the order parameter for a wide range of interaction strengths. We discuss the emergence of a "sign problem" for more general dynamical correlators and setups.

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

0 major / 2 minor

Summary. The manuscript introduces a Monte Carlo sampling scheme to numerically evaluate the Lehmann representation (and Quench Action formalism) for time-dependent expectation values of local operators after homogeneous quenches in interacting integrable models. It reports benchmarks showing excellent agreement with exact results for non-interacting lattice and continuum models as well as short-time weak-interaction regimes, followed by an application to the order-parameter dynamics in the repulsive Lieb-Liniger model after a quench from a Bose-Einstein condensate. Limitations such as the emergence of a sign problem for more general dynamical correlators are explicitly discussed.

Significance. If the central numerical method holds, the work provides a practical route to system sizes and evolution times beyond the reach of existing techniques for local observables in integrable systems. The parameter-free benchmarks against independent exact solutions and the transparent treatment of the sign-problem limitation constitute clear strengths that support the method's utility for the targeted class of problems.

minor comments (2)
  1. The relation between the full Lehmann sum and the Quench Action implementation could be stated more explicitly in the methods section to aid readers unfamiliar with the latter formalism.
  2. Figure captions for the Lieb-Liniger results should include the precise range of interaction strengths and the number of Monte Carlo samples used to allow direct reproducibility assessment.

Simulated Author's Rebuttal

0 responses · 0 unresolved

We thank the referee for their positive assessment of the manuscript, recognition of its strengths in benchmarks and transparent discussion of limitations, and recommendation to accept.

Circularity Check

0 steps flagged

No significant circularity identified

full rationale

The paper introduces a Monte Carlo sampling algorithm to evaluate the Lehmann representation (or Quench Action) for time-dependent local operator expectations after quenches in integrable models. Its central claim is the existence and efficiency of this numerical scheme for the targeted class of observables, which is directly benchmarked against independent exact solutions for non-interacting lattice and continuum cases plus short-time weak-interaction analytics. No load-bearing step reduces by construction to a fitted parameter, self-citation chain, or ansatz smuggled from prior work by the same authors; the reported quantities are obtained from the sampling procedure itself and cross-validated externally rather than being equivalent to the inputs by definition.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

The approach rests on standard properties of integrable models and Monte Carlo sampling rather than new postulates. No free parameters are fitted to the target data; interaction strength is an input varied across runs.

axioms (2)
  • standard math The Lehmann representation converges to the correct time-dependent expectation value when summed over the complete basis of eigenstates.
    Invoked in the description of the Monte Carlo sampling scheme for the full Lehmann sum.
  • domain assumption Integrability permits an efficient representation of the post-quench state via the Quench Action formalism.
    Used to accommodate both the full sum and Quench Action in the sampling procedure.

pith-pipeline@v0.9.0 · 5673 in / 1396 out tokens · 44466 ms · 2026-05-20T03:47:03.684205+00:00 · methodology

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Reference graph

Works this paper leans on

77 extracted references · 77 canonical work pages · 2 internal anchors

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