{"id":"843dd29c-c9fa-4fdf-949e-32ff32612f05","arxiv_id":"2506.05989","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":4.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":3,"one_line_summary":"Continuous-wave Raman conversion in a hydrogen-filled hollow-core fiber shifts 914 nm light to the telecom S-band with 0.27% internal efficiency and identifies a path toward much higher efficiency.","lead":"Researchers converted 914 nm laser light to 1474 nm telecom-band light inside a hydrogen-filled hollow-core fiber using continuous-wave lasers. The conversion efficiency is currently about 0.27%, and the paper maps the losses that must be fixed to make such a frequency shifter practical for quantum networks.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Parasitic Raman backgrounds may be included in the efficiency data; without explicit subtraction, the 0.27% efficiency and L² scaling are not yet established.","rationale":"The paper is a careful experimental study with transparent loss characterization and a reasonable physical model. However, the central quantitative claims—measured internal efficiency of 0.27% and the fitted length-scaling coefficient 0.0044(6)%/(W²m²)—are only meaningful if the detected 1474 nm count rate is due to CSRS signal rather than to the parasitic Raman lines the authors themselves identify in Section III B 3. The manuscript never states that the efficiency data were background-subtracted, and the 'removal' of that background is described only as a future improvement ('To remove this background, very narrow bandpass filters or filter cavities can be used'). At the low probe powers typical for frequency-conversion tests, the quoted pump-only background rates (~10⁶ cps) can easily be comparable to or exceed the signal photon rate, which would bias ηmax upward and distort the length-scaling fit because the background depends on pump power and pump attenuation, not on the probe-to-signal conversion process. Other concerns, such as the extrapolation to 70% at 21 m, are explicitly speculative and not central to the demonstrated result. The most direct resolution is an explicit statement or a control measurement of the background at the exact operating points used in Fig. 3, followed by a background-subtracted re-fit. Because this is an addressable experimental detail rather than a demonstrated fatal flaw, the reader's CONDITIONAL verdict remains appropriate.","tokens_in":8783,"tokens_out":6307,"duration_ms":62080,"concrete_test":"At each fiber length and pump power used in Fig. 3, measure the 1474 nm APD count rate with the 914 nm probe blocked, then with the probe present, and subtract the blocked-probe rate from the total. Re-fit Eq. 1 to the background-subtracted data and compare the fitted coefficient and ηmax with 0.0044(6)%/(W²m²) and 0.27%; if the values shift by more than the quoted 1σ uncertainties, the central length-scaling and efficiency claims are not robust. The authors can perform this check on their existing data or state whether it was already performed.","verdict_should_be":"UNCHANGED","load_bearing_attack":"To establish ηmax=0.27% and the L²-length-scaling coefficient 0.0044(6)%/(W²m²), the detected 1474 nm rate must be attributable to the CSRS signal. Section III B 3 documents two parasitic hydrogen Raman lines at 1468.6 nm and 1469.3 nm that pass the 25 nm bandpass filter, producing backgrounds of ~7×10⁵ cps (942 nm pump at 4 W) and ~5.5×10⁵ cps (1550 nm pump at 12.5 W), each appearing without the probe. The paper never states whether the efficiency data in Fig. 3 and the ηmax value were corrected by subtracting these backgrounds. Because the background is independent of the 914 nm probe, it contributes a rate offset rather than a fraction; at the low probe photon rates typical of frequency-conversion tests, this offset can dominate the apparent signal. If uncorrected, both the absolute efficiency and the shape of the efficiency-vs-length curve (which is affected by pump attenuation over length) would be distorted, so the central claim is not yet fully supported.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports continuous-wave coherent Stokes/anti-Stokes Raman scattering (CSRS) frequency conversion from 914 nm to 1474 nm in a hydrogen-filled anti-resonant hollow-core fiber. The authors present cut-back measurements at four fiber lengths, extract a length-scaling coefficient of 0.0044(6) %/(W^2 m^2), and report a maximum internal efficiency of 0.27% at pump powers of 3.87 W (942 nm) and 12.6 W (1550 nm). They also characterize transmission losses for the three input fields, study bend-loss effects on the optimal pressure, and identify two parasitic hydrogen Raman lines at 1468.6 nm and 1469.3 nm that pass the detection bandpass filter. The paper closes with an extrapolation to a 21 m fiber that would yield 70% conversion efficiency under assumed loss parameters.","tokens_in":8999,"tokens_out":4598,"duration_ms":48083,"significance":"The central experimental result is potentially valuable for quantum frequency conversion in the telecom band, since it demonstrates few-per-mille conversion efficiency with continuous-wave pumps in a gas-filled hollow-core fiber and identifies a path toward longer interaction lengths. The paper has several concrete strengths: the cut-back efficiency data are compared with a standard model (Eq. 1) corrected for measured transmission losses, the parasitic Raman lines are identified using HITRAN data with quantitative background rates, and the bend-loss analysis connects the operating pressure to the fiber geometry. However, the quantitative claims of 0.27% efficiency and quadratic length scaling currently hinge on an unstated background-subtraction procedure for the parasitic Raman lines, and on a fit to only four fiber lengths. If the background subtraction is clarified and the scaling analysis is made more explicit, the work would be a solid incremental contribution; as written, the central numbers are not fully established.","major_comments":[{"comment":"The text reports parasitic Raman backgrounds of approximately 7e5 cps from the 942 nm pump and 5.5e5 cps from the 1550 nm pump at 1468.6 nm and 1469.3 nm, respectively, both within the 25 nm bandpass filter. However, the paper never states whether the efficiency data in Fig. 3 and the quoted eta_max = 0.27% were corrected by subtracting these backgrounds. Since the efficiency is defined as the detected 1474 nm photon rate divided by the incoming 914 nm photon rate, an uncorrected constant background would inflate the apparent efficiency and, because the background is independent of the probe, it would distort the length-dependence curve. Please state explicitly whether and how this background was subtracted, and provide the uncertainty that includes the subtraction.","section":"Section III B 3 and Fig. 3"},{"comment":"The quadratic length-scaling claim rests on a fit to only four cut-back lengths (1.85, 1.47, 1.16, and 0.27 m), with the shortest point obtained for an unwound fiber under different bend conditions. The manuscript does not report the fit residuals, the uncertainty in the fitted exponent, or a comparison with a linear or saturation model. Please report the full fit details, including which losses were corrected and how, the confidence interval of the scaling exponent, and a sensitivity check that shows whether the conclusion changes when the 0.27 m point is excluded.","section":"Section III A and Fig. 3"},{"comment":"The definition of 'internal efficiency' is ambiguous. The measurement is a detected photon rate on an APD with 10% detection efficiency and an approximately 270 cps dark count rate, but the paper does not state whether the quoted efficiencies include corrections for APD efficiency, output coupling, filtering, and dark-count subtraction. Because eta_max = 0.27% is the headline result, the exact conversion between the measured photon rate and the reported efficiency should be given explicitly.","section":"Section III A and Section II"}],"minor_comments":[{"comment":"The text says 'the fourth fiber of 0.27(20) m length', which is inconsistent with the stated length 0.27(2) m in Section III A and in the Fig. 5 caption; this appears to be a typographical error and should be corrected.","section":"Section III B 2"},{"comment":"There are typographical errors in the conclusion ('otical components') and in the Fig. 7 caption ('Schemtic overview'), which should be fixed.","section":"Section IV and Fig. 7"},{"comment":"The capillary wall thickness is inferred by matching the optimal-pressure data to the Zeisberger model, and the same model is then used to discuss phase matching; the paper should state explicitly that this is not an independent validation of the wall thickness.","section":"Section II and Section III B 1"},{"comment":"The 70% efficiency projection for a 21 m fiber assumes quadratic scaling, 83% incoupling, 15.9 dB/km attenuation at all wavelengths, and unchanged parasitic backgrounds; these assumptions should be labeled explicitly as an idealized extrapolation rather than a measured expectation, and a sensitivity estimate would improve the clarity.","section":"Section IV"},{"comment":"The figure would benefit from error bars on the data points and from a clear indication of which points are raw measured efficiencies and which are corrected for transmission losses.","section":"Fig. 3"}],"recommendation":"major_revision","confidential_remarks":"The manuscript describes a useful experimental advance, but the missing statement on background subtraction is the key issue that prevents acceptance. If the authors confirm that the efficiencies were background-subtracted and provide the requested fit details, the paper would likely be publishable as a solid incremental result. The paper's strengths are the careful identification of parasitic Raman lines, the cut-back methodology, and the use of standard theoretical models; the main weakness is the lack of clarity in defining the measured efficiency."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Do you remember the paper from the Bonn group on CW Raman conversion in hydrogen-filled hollow-core fiber? I read it with the stress-test list in hand. Bottom line: it's a genuine experimental study with useful new data, but the central efficiency numbers have a couple of unresolved problems that need fixing before I would trust them.\n\nWhat's good: cut-back measurement over four lengths (0.27–1.85 m) with transmission-loss corrections, giving a length-dependence curve that should test Eq. 1. The identification of two parasitic hydrogen Raman lines (1-0 O(2) from 942 nm, 0-0 S(0) from 1550 nm) that leak through the 25 nm filter is clearly explained and practically important. The bend-radius dependence of the optimal pressure is also new and useful for anyone packaging these fibers.\n\nNow the soft spots, in proportion. First, the stress-test concern is real: the paper documents backgrounds of ~7×10^5 cps and ~5.5×10^5 cps from the two pumps, but never says whether the efficiency data (Fig. 3 and ηmax = 0.27%) were background-subtracted. Since the probe is attenuated and the signal rates can be comparable to these backgrounds, this is not a footnote; it's the difference between \"measured\" and \"inferred.\" That's an addressable omission, but it has to be addressed.\n\nSecond, and more worrying, the numbers in Sec. III A and IV don't line up. A scaling of 0.0044 %/(W²m²) predicts η/P1P2 = 0.015 %/W² at L = 1.85 m. The text quotes a fitted internal efficiency of 0.0060(13) %/W² at that length, and the y-axis of Fig. 3 tops out around 0.007. Those can't both be right. The 1.9% projection and the 70% route are built on the 0.0044 number; if that's wrong, the route is optimistic by a factor of ~2.5. If the 0.0060 number is right, then the quoted scaling is too large. Either way, there's a contradiction that needs a correction.\n\nThe near-unity route also rests on untested assumptions (21 m fiber, uniform losses), but that's clearly labeled as a route, so I'm less concerned.\n\nWho should read this: experimentalists in frequency conversion; they'll want the parasitic-line analysis and the bend-radius data. It deserves peer review, but I would ask for a revised version that resolves the subtraction issue and reconciles the quoted efficiencies before citing it.\n\nFor the reading group, I'd say maybe—the contradiction is a good exercise in checking numbers.","headline":"A useful CW Raman conversion study, but the efficiency claims are undermined by an unstated background-subtraction question and an internal inconsistency in the quoted scaling.","tokens_in":9518,"tokens_out":10128,"would_cite":false,"duration_ms":85585,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":["42.65.Dr"],"model":"deepseek-v4-flash","headline":"Continuous-wave lasers in a hydrogen-filled hollow-core fiber convert 914-nm probe photons to 1474-nm telecom light with 0.27% internal efficiency, and the conversion efficiency grows quadratically with fiber length.","keywords":["quantum frequency conversion","coherent Stokes Raman scattering","hollow-core fiber","molecular hydrogen","continuous-wave pump","telecom S-band","Raman background","frequency conversion efficiency"],"falsifier":"Switch off the $914$-nm probe and count photons at $1474$ nm through a filter narrower than $1$ nm, repeating the measurement with each pump blocked in turn: if the $1474$-nm photon rate does not fall to near the APD dark count of about $270$ per second, or if the fitted length scaling changes after narrow-band filtering, then the reported $0.27\\%$ efficiency and $0.0044(6)\\,\\%/(\\mathrm{W}^2\\,\\mathrm{m}^2)$ scaling include parasitic Raman background rather than pure CSRS signal.","tokens_in":8558,"feed_emoji":"⚛️","tokens_out":22471,"duration_ms":181835,"temperature":0.7,"pith_summary":"The paper claims that a hydrogen-filled hollow-core fiber (a fiber that guides light through a gas-filled core rather than through glass) driven by two continuous-wave pump lasers can act as a frequency shifter for quantum-network photons, converting $914$-nm probe light into $1474$-nm telecom S-band light while preserving polarization. The new result is that the internal conversion efficiency grows quadratically with fiber length over the tested range of $0.27$ m to $1.85$ m, with a fitted scaling of $0.0044(6)\\,\\%/(\\mathrm{W}^2\\,\\mathrm{m}^2)$ and a best measured internal efficiency of $0.27\\%$ at the maximum available pump powers. The paper also quantifies what limits longer fibers: propagation loss at the probe wavelength, bend loss that shifts the optimum pressure, and two parasitic hydrogen Raman lines that inject background counts near the signal wavelength. If the claims hold, this is a route toward state-preserving single-photon frequency conversion with continuous-wave sources rather than pulsed lasers, which matters because quantum networks need photons converted between incompatible wavelength bands without disturbing their quantum state.","feed_headline":"Continuous-wave light converts 914-nm photons to telecom at 0.27%","feed_subtitle":"Quantum networks need state-preserving wavelength conversion; this CW gas-fiber route scales with length.","key_machinery":"The central mechanism is coherent Stokes Raman scattering (CSRS) driven by a molecular coherence in hydrogen: two continuous-wave pumps at $1550$ nm and $942$ nm, whose beat note matches the $Q_1(1)$ vibrational transition at $125$ THz, write a coherence that converts the $914$-nm probe into the $1474$-nm signal. The workhorse identity is the efficiency scaling $\\eta \\propto |\\chi^{(3)}(\\omega)|^2 L^2 \\operatorname{sinc}^2(\\Delta\\beta(p) L/2)\\, I_{\\mathrm{pump1}}I_{\\mathrm{pump2}}$, where the phase mismatch $\\Delta\\beta$ is computed from propagation constants built on the analytic dispersion model for anti-resonant hollow-core fibers (Ref. [28]); the cut-back procedure isolates the $L^2$ factor of this formula. Secondary machinery includes the critical bend radius $R_{l,m}$ for capillary-mode coupling, a saturation curve $p_{\\mathrm{opt}} = p_{\\max}(1-e^{-b(r-r_0)})$ fitted to the optimum-pressure data, and molecular line assignments that identify the parasitic background lines.","core_discovery":"On its own terms, the paper's central claim is experimental: in a commercial anti-resonant hollow-core fiber filled with hydrogen at high pressure, two continuous-wave pump fields whose frequency difference matches the $Q_1(1)$ vibrational transition of molecular hydrogen at $125$ THz drive a coherent Stokes Raman scattering (CSRS) process that converts a $914$-nm probe photon into a $1474$-nm signal photon. The authors cut the fiber back to lengths of $1.85$ m, $1.47$ m, $1.16$ m, and $0.27$ m and fit the expected $\\eta \\propto |\\chi^{(3)}|^2 L^2 \\operatorname{sinc}^2(\\Delta\\beta L/2)\\, I_{\\mathrm{pump1}}I_{\\mathrm{pump2}}$ dependence, corrected for measured transmission losses, obtaining a length-scaling coefficient of $0.0044(6)\\,\\%/(\\mathrm{W}^2\\,\\mathrm{m}^2)$; at the maximum available pump powers of $3.87$ W and $12.6$ W they infer an internal efficiency of $\\eta_{\\max} = 0.27\\%$. The paper further reports that the optimum phase-matching pressure rises with bend radius and saturates above roughly $30$ cm, and that two parasitic Raman transitions of hydrogen produce background photons at $1468.6$ nm and $1469.3$ nm that pass the $25$-nm bandpass filter.","pith_inferences":["An implication the authors leave implicit: the reported $0.27\\%$ internal efficiency may include counts from the two parasitic Raman lines, so until narrow-band filtering confirms otherwise, the honest reading is that $0.27\\%$ is an upper bound on the CSRS signal conversion.","The same $Q_1(1)$ coherence should translate any probe wavelength by the fixed $125$-THz shift, making this pair one instance of a general continuous-wave-driven translator across the near-infrared-to-telecom window.","The $21$-m, $70\\%$ projection extrapolates a quadratic law measured only up to $1.85$ m; measuring at intermediate lengths of roughly $5$ m and $10$ m in the lower-loss fiber would test the extrapolation before building a full-scale device."],"forward_implications":["If the quadratic length scaling holds beyond $1.85$ m, lengthening the fiber at the same pump powers is a direct route to efficiencies above $1\\%$, and the paper projects about $70\\%$ for a $21$-m fiber with lower losses.","The process preserves polarization and runs on continuous-wave lasers, so a quantum-network node needing state-preserving conversion between the near-infrared and the telecom S-band could use this scheme without pulsed sources.","Propagation loss at the probe wavelength ($0.93(37)$ dB/m at $914$ nm) dominates the total, so shifting the fiber's capillary-wall resonance away from $914$ nm is the clearest single improvement.","Bend radii below about $10$ cm destroy coupling to the $LP_{01}$ mode entirely, and resonant bend losses set in below a critical radius of about $24$ cm, which constrains how tightly the fiber can be packaged.","Because the parasitic $1468.6$-nm and $1469.3$-nm lines pass the $25$-nm bandpass filter, a deployed device needs narrow-band filtering or a different signal wavelength to reach low-background operation."],"supporting_citations":[{"why":"The same experimental system as this work; supplies the prior power-scaling, polarization, incoupling, and background results that the length cut-back extends.","marker":"[27]"},{"why":"Earlier continuous-wave frequency conversion in a hydrogen-filled hollow-core fiber that established the apparatus and pressure-handling approach.","marker":"[26]"},{"why":"The analytic dispersion model for anti-resonant hollow-core fibers, used to compute the effective refractive index, phase matching, and optimum pressure.","marker":"[28]"},{"why":"The tutorial that supplies the coherent Raman scattering efficiency scaling used in Eq. 1, quadratic in length and in both pump intensities.","marker":"[20]"},{"why":"Pulsed single-photon frequency conversion in hydrogen that sets the performance benchmark against which the 70 percent projection is compared.","marker":"[10]"},{"why":"The molecular spectroscopic database used to assign the parasitic 1-0 O(2) and 0-0 S(0) hydrogen lines that create background near 1474 nm.","marker":"[36]"}],"fun_headline_variants":["CW pumps shift 914-nm photons to telecom at 0.27%","Gas-filled fiber converts 914-nm photons to telecom with CW pumps","0.27% efficiency: CW pumps shift photons to telecom in fiber","CW-driven Raman conversion reaches telecom band in hydrogen fiber","Hollow-core fiber with CW pumps converts 914-nm to 1474-nm"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The quoted efficiencies and the length-scaling fit assume that every detected photon at $1474$ nm is genuine signal, but the paper does not state whether the roughly one million counts per second of background from two parasitic hydrogen Raman lines at $1468.6$ nm and $1469.3$ nm were subtracted before the efficiencies were computed.","fun_headline_variants_meta":{"raw":{"variants":["CW pumps shift 914-nm photons to telecom at 0.27%","Gas-filled fiber converts 914-nm photons to telecom with CW pumps","0.27% efficiency: CW pumps shift photons to telecom in fiber","CW-driven Raman conversion reaches telecom band in hydrogen fiber","Hollow-core fiber with CW pumps converts 914-nm to 1474-nm"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000912,"raw_usage":{"total_tokens":3903,"prompt_tokens":913,"completion_tokens":2990,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":529,"completion_tokens_details":{"reasoning_tokens":2892}},"tokens_in":529,"tokens_out":2990,"duration_ms":21329,"temperature":1.0,"reasoning_tokens":2892,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-07T06:02:50.893817+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Switch off the $914$-nm probe and count photons at $1474$ nm through a filter narrower than $1$ nm, repeating the measurement with each pump blocked in turn: if the $1474$-nm photon rate does not fall to near the APD dark count of about $270$ per second, or if the fitted length scaling changes after narrow-band filtering, then the reported $0.27\\%$ efficiency and $0.0044(6)\\,\\%/(\\mathrm{W}^2\\,\\mathrm{m}^2)$ scaling include parasitic Raman background rather than pure CSRS signal.","supporting_citations":[{"cited_title":"Javadi, I","cited_arxiv_id":null,"evidence_quote":"The same experimental system as this work; supplies the prior power-scaling, polarization, incoupling, and background results that the length cut-back extends."},{"cited_title":"Gonzalez-Raya, A","cited_arxiv_id":null,"evidence_quote":"Earlier continuous-wave frequency conversion in a hydrogen-filled hollow-core fiber that established the apparatus and pressure-handling approach."},{"cited_title":"Aghababaei, C","cited_arxiv_id":null,"evidence_quote":"The analytic dispersion model for anti-resonant hollow-core fibers, used to compute the effective refractive index, phase matching, and optimum pressure."},{"cited_title":"Characterization of near-infrared to telecom frequency conversion in a rubidium-filled hollow-core photonic-crystal fiber","cited_arxiv_id":"2412.13418","evidence_quote":"The tutorial that supplies the coherent Raman scattering efficiency scaling used in Eq. 1, quadratic in length and in both pump intensities."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Pulsed single-photon frequency conversion in hydrogen that sets the performance benchmark against which the 70 percent projection is compared."},{"cited_title":"Yu and J","cited_arxiv_id":null,"evidence_quote":"The molecular spectroscopic database used to assign the parasitic 1-0 O(2) and 0-0 S(0) hydrogen lines that create background near 1474 nm."}],"review_version":1}