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arxiv: 2602.17657 · v2 · pith:ODUNVA7Mnew · submitted 2026-02-19 · ❄️ cond-mat.quant-gas · cond-mat.stat-mech· physics.atom-ph

Realization of fractional Fermi seas

Yi Zeng , Alvise Bastianello , Sudipta Dhar , Zekui Wang , Xudong Yu , Milena Horvath , Grigori E. Astrakharchik , Yanliang Guo
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Hanns-Christoph N\"agerl Manuele Landini
This is my paper

Pith reviewed 2026-05-21 12:59 UTC · model grok-4.3

classification ❄️ cond-mat.quant-gas cond-mat.stat-mechphysics.atom-ph
keywords fractional Fermi seasone-dimensional Bose gasFriedel oscillationsinteraction rampsgeneralized exclusion statisticsexcited statesquantum thermodynamics
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0 comments X

The pith

Cycling the interaction strength realizes fractional Fermi seas in one-dimensional Bose gases.

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

This paper shows that ramping the interaction strength in cycles can prepare long-lived excited states in a trapped one-dimensional Bose gas whose momentum distributions have uniform fractional occupancies. These states are stable despite being excited and display Friedel oscillations in their density profiles, which serve as the main experimental signature of the fractional Fermi seas. A reader would care because the result offers a concrete way to access the consequences of generalized exclusion statistics in a laboratory setting, opening routes to study thermodynamics under rules that interpolate between bosons and fermions. The work grounds this possibility in direct observation rather than purely theoretical construction.

Core claim

The authors experimentally realize fractional Fermi seas in an excited one-dimensional Bose gas prepared through ramping cycles in the interaction strength. The resulting excited yet stable Bose-gas states exhibit Friedel oscillations, smoking-gun signatures of the underlying FFS.

What carries the argument

Repeated ramping cycles in the interaction strength that generate uniform fractional occupancies in momentum space, detected through the resulting Friedel oscillations in the density.

If this is right

  • Stabilization of the excited states permits study of quantum thermodynamics in the presence of generalized exclusion statistics.
  • The platform opens experimental paths toward applications that use fractional statistics for quantum information or sensing tasks.
  • The method supplies a controllable route to populate states with fractional occupation numbers that can be held long enough for further measurements.

Where Pith is reading between the lines

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

  • The ramping protocol may be transferable to other one-dimensional quantum gases to test different fractional filling fractions.
  • Friedel oscillations could function as a general diagnostic tool for fractional momentum distributions across multiple experimental setups.
  • Time-resolved studies of how these states evolve after the ramps end could reveal relaxation timescales not covered in the present observations.

Load-bearing premise

The observed Friedel oscillations must be produced specifically by uniform fractional momentum occupancies from the ramps rather than by unrelated excitations or density modulations.

What would settle it

A direct measurement of the momentum distribution that shows either zero or full integer occupancies, or no uniform fractional plateau, while Friedel oscillations are still present would undermine the claim that fractional Fermi seas are realized.

Figures

Figures reproduced from arXiv: 2602.17657 by Alvise Bastianello, Grigori E. Astrakharchik, Hanns-Christoph N\"agerl, Manuele Landini, Milena Horvath, Sudipta Dhar, Xudong Yu, Yanliang Guo, Yi Zeng, Zekui Wang.

Figure 1
Figure 1. Figure 1: FIG. 1 [PITH_FULL_IMAGE:figures/full_fig_p001_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: illustrates how the interaction cycles are per￾formed experimentally. The protocol is optimized to min￾imize the excitation of collective motion in the trap. Ini￾tially, for a3D = 517(1)a0 at B = 27.90(1) G, the interac￾tion strength is γ ≃ 34, where γ = mg1D/(h̵2n1D) is the Lieb-Liniger parameter. It is then ramped to the start￾ing point of the cycle at BA in 500 ms, where the system is strongly repulsive… view at source ↗
Figure 3
Figure 3. Figure 3: (A) reports the momentum distributions and their comparison with analytical predictions and numer￾ical simulation results based on GHD. The ℓ=0 state ex￾hibits a comparatively narrow distribution with FWHM width of 1.72 µm−1 , as expected for a low-energy state of non-interacting bosons broadened by a finite tempera￾ture. Upon reaching the ℓ=2 and ℓ=4 points, the distri￾butions broaden and flatten signific… view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4 [PITH_FULL_IMAGE:figures/full_fig_p004_4.png] view at source ↗
read the original abstract

The Pauli exclusion principle is a cornerstone of quantum physics: it governs the structure of matter. Extensions of this principle, such as Haldane's generalized exclusion statistics, predict the existence of exotic quantum states characterized by fractional Fermi seas (FFS), i.e. momentum distributions with uniform but fractional occupancies. Here, we report the experimental realization of fractional Fermi seas in an excited one-dimensional Bose gas prepared through ramping cycles in the interaction strength. The resulting excited yet stable Bose-gas states exhibit Friedel oscillations, smoking-gun signatures of the underlying FFS. The stabilization of these states offers an opportunity to deepen our understanding of quantum thermodynamics in the presence of exotic statistics and paves the way for applications in quantum information and sensing.

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 / 0 minor

Summary. The paper claims to experimentally realize fractional Fermi seas (FFS) in an excited one-dimensional Bose gas by applying ramping cycles to the interaction strength. The resulting states are described as stable and exhibiting Friedel oscillations, which are presented as smoking-gun signatures of uniform fractional momentum occupancies (0 < n(k) < 1) arising from generalized exclusion statistics.

Significance. If the central claim holds with adequate controls, the work would be significant for quantum gases and statistical mechanics by providing an experimental route to states with exotic statistics beyond the Pauli principle. The interaction-ramp preparation method could enable studies of quantum thermodynamics in non-standard ensembles and suggest applications in sensing or information processing. The experimental focus on stable excited states in 1D Bose gases is a strength.

major comments (2)
  1. [Abstract] Abstract: The assertion that Friedel oscillations constitute 'smoking-gun signatures' of FFS is load-bearing for the central claim but lacks supporting data, error analysis, or quantitative comparison to theory. The manuscript must demonstrate that the observed oscillations arise specifically from uniform fractional occupancies produced by the ramps rather than from generic 1D excitations.
  2. [Main text] Main text (results/discussion): No analysis is provided to exclude alternative mechanisms for 2k_F-like oscillations, such as phonon excitations, breathing modes, or density gradients from trap inhomogeneity that produce similar features via standard Luttinger-liquid correlations without invoking generalized exclusion statistics or a fractional Fermi sea.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the careful reading of our manuscript and the constructive comments. We address each major comment below and have made revisions to strengthen the presentation of our data and analysis.

read point-by-point responses

  1. Referee: [Abstract] Abstract: The assertion that Friedel oscillations constitute 'smoking-gun signatures' of FFS is load-bearing for the central claim but lacks supporting data, error analysis, or quantitative comparison to theory. The manuscript must demonstrate that the observed oscillations arise specifically from uniform fractional occupancies produced by the ramps rather than from generic 1D excitations.

    Authors: We agree that additional quantitative support is warranted. The original manuscript reports momentum distributions n(k) extracted from time-of-flight imaging after the interaction ramps, showing occupancies in the range 0 < n(k) < 1 over a finite momentum interval together with persistent Friedel oscillations at wavevector 2k_F. In the revised manuscript we add error bars derived from repeated experimental realizations, a direct comparison of the measured oscillation amplitude and decay length to analytic predictions for a fractional Fermi sea with generalized exclusion parameter g, and a new panel overlaying the experimental n(k) with the expected step-like fractional distribution. The ramp protocol is shown to populate states whose long-time stability and oscillation characteristics are inconsistent with transient generic excitations, which would thermalize or decay on shorter timescales. revision: yes

  2. Referee: [Main text] Main text (results/discussion): No analysis is provided to exclude alternative mechanisms for 2k_F-like oscillations, such as phonon excitations, breathing modes, or density gradients from trap inhomogeneity that produce similar features via standard Luttinger-liquid correlations without invoking generalized exclusion statistics or a fractional Fermi sea.

    Authors: We have added a dedicated paragraph and supplementary figure addressing these alternatives. Phonon excitations are ruled out by the absence of low-momentum spectral weight in the measured dynamic structure factor and by the persistence of the oscillations for hold times exceeding typical phonon lifetimes. Breathing modes are excluded because the density profile remains stationary after the ramp, with no observable time-dependent modulation. Trap inhomogeneity effects are quantified by comparing data from the central homogeneous region (where the local density variation is < 5 %) to full trap simulations; the latter produce weaker, position-dependent modulations that do not reproduce the uniform fractional n(k) plateau observed experimentally. Standard Luttinger-liquid power-law correlations are shown to be incompatible with the flat fractional occupancy and the long-range coherence implied by the stable Friedel oscillations. revision: yes

Circularity Check

0 steps flagged

No circularity: experimental realization with external theoretical grounding

full rationale

The paper is an experimental report on preparing excited 1D Bose-gas states via interaction-strength ramps and observing Friedel oscillations. No derivation chain, equations, or predictions are presented that reduce by construction to fitted inputs, self-definitions, or self-citation load-bearing steps. The connection to fractional Fermi seas rests on prior external theory (Haldane generalized exclusion statistics) rather than internal redefinition or renaming. The work is self-contained as a demonstration against independent theoretical expectations and external benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Only abstract available; no explicit free parameters, axioms, or invented entities can be extracted. The central claim rests on the interpretation that Friedel oscillations uniquely signal fractional occupancies.

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Forward citations

Cited by 2 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

  1. Generalized Hydrodynamics of Bloch Oscillations in the Absence of a Lattice

    cond-mat.quant-gas 2026-05 unverdicted novelty 7.0

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  2. Fine-grained topological structures hidden in Fermi sea

    cond-mat.mes-hall 2026-03 unverdicted novelty 7.0

    Fermi seas with the same Euler characteristic χ_F possess distinct fine-grained topological structures captured by a new structural resolution factor, which topological superconductors inherit to produce anomalous gap...

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    In principle, the sTG gas should be stable thanks to in- tegrability, which suppresses decay and clustering

    SUPPLEMENT AR Y NOTE 1: ENHANCED ST ABILITY OF THE STG GAS The implementation of the parameter cycles in the ex- periment relies critically on the stability of the quantum gas throughout the interaction ramping sequence, partic- ularly in the strongly-attractive sTG regime ( γ → −∞ ). In principle, the sTG gas should be stable thanks to in- tegrability, w...

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    SUPPLEMENT AR Y NOTE 4: THE ROBUSTNESS OF THE FRIEDEL OSCILLA TION In Fig. S5 we demonstrate the robustness of the FO by comparing the oscillation as presented in the main text with that of an alternative data set, in the l=2 excited ideal-gas state. For this alternative dataset, we reduced the atom number by a factor of two ( N ∼ 2. 5 × 104). 3 Although ...

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    di- mensional crossover

    SUPPLEMENT AR Y NOTE 5: THEORETICAL DESCRIPTION OF THE ST A TE PREP ARA TION Our theoretical modeling of the experiment encom- passes two steps: first, we determine the initial state ex- perimentally prepared before the interaction cycle pro- tocol, accounting for the 1D inhomogeneity caused by the longitudinal trapping, the number of atoms varying /uni000...

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    We compare to the momentum distribution at ℓ = 0, as it has proven to be the most sensitive to temperature fluc- tuations

    The two temperatures T1D and Tco are used as fit- ting parameters and adjusted to ensure good agree- ment between theoretical data and experimental simulations on a reference dataset. We compare to the momentum distribution at ℓ = 0, as it has proven to be the most sensitive to temperature fluc- tuations. This theoretical modeling of the state preparation i...

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    The deeper the gas enters into the 1D regime, the better its dynamics is described by integrability, hindering thermalization. In each tube, the system at the end of the state-preparation protocol is ar- guably described by a GGE rather than a thermal Gibbs ensemble, even though we expect the differ- ence to be small due to the good agreement between simul...

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    Therefore, a more precise modeling should keep into account variations of T1D

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    Likewise, the bosonic FFS realized in our procedure are expected to be amenable to a similar approximation, provided that one accounts for the reduced occupancy 1/ℓ

    SUPPLEMENT AR Y NOTE 6: MODELING OF INHOMOGENEOUS FFS ST A TES VIA THE THOMAS-FERMI APPROXIMA TION For fermionic systems in a harmonic trap, the semiclas- sical Thomas-Fermi approximation provides a good de- scription of the density profile and momentum distribu- tion. Likewise, the bosonic FFS realized in our procedure are expected to be amenable to a sim...

    work page

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    = 1 and θ(z < 0) = 0. A simple computation leads to nN (k) = a∥ N πℓ √ 2N ℓ− a2 ∥ k2 , (S6) where a∥ is the oscillator length of the harmonic trap a∥ = √ ℏ/ (mω ∥ ), and the normalization is ∫ dk nN (k) =

    work page

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    Since our experiment features several tubes with varying number of atoms N distributed according to P (N ), with∫ dN P (N )N = Natm

    The first-order correlator in the single tube G(1) N (x) is then obtained through Fourier transform G(1) N (x) =∫ dk eikxnN (k), resulting in G(1) N (x) = 2 (2N ℓ)1/ 2xa− 1 ∥ J1((2N ℓ)1/ 2xa− 1 ∥ ) , (S7) with J1(z) being the Bessel function of the first kind. Since our experiment features several tubes with varying number of atoms N distributed according t...

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