{"id":"823d5c1c-0058-4874-ada3-83747938f757","arxiv_id":"2602.00253","paper_version":2,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":0,"one_line_summary":"O-band polarization entanglement was distributed over a 24.4-km deployed fiber link with no measurable fidelity loss while coexisting with a fully-loaded C-band classical system carrying 1.6 Tbps.","lead":"A team at Northwestern and StarLight shows that polarization-entangled photons can be sent over 24.4 km of installed fiber while very bright, standard telecom data signals travel on the same fiber, with the quantum link barely affected. The result is a step toward putting quantum networking on the same fibers that already carry the internet.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The 36.8-Tbps extrapolation rests on an untested equivalence between ASE and data-modulated C-band channels; the measured coexistence fidelity itself is sound.","rationale":"The reader correctly identified the unverified equivalence between ASE-filled and data-modulated C-band channels as the weakest point. My stress-test confirms this: the paper's empirical core—entanglement fidelity preserved under an actual fully-loaded C-band OLS with 21.4 dBm aggregate power on deployed fiber—is convincingly demonstrated, with clean comparisons and appropriate filtering. The 36.8-Tbps generalization, however, is not an experimental result but a physical assumption about SpRS scaling. Because the paper itself states 'total transmitted classical power over a constant wavelength span is the relevant variable' and relies on the power spectrum remaining constant regardless of channel population, the check reduces to whether per-slot average power equality is sufficient. That is plausible for average SpRS, but it is not tested, and slight violations would change the headline extrapolation without changing the measured fidelity. The novelty/first claims are also literature-dependent but not correctness issues. The statistical-only error bars are a minor concern, not disqualifying. Therefore the conditional verdict stands; no change is needed.","tokens_in":15104,"tokens_out":5866,"duration_ms":79421,"concrete_test":"Reproduce the coexistence measurement with the C-band populated only by modulated data channels—e.g., use the same Ciena OLS to generate 16 or 40 800-Gbps channels occupying the same 4.9-THz span at the same 21.4-dBm aggregate launch power—and compare (i) the SpRS count rate at 1290 nm and (ii) the Bell-state fidelity against the ASE-filled case. If both match within the reported errors, the 36.8-Tbps extrapolation is supported; if either shifts, the no-impact claim must be restricted to the measured channel population.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The directly measured result—94.2±0.4% Bell-state fidelity under the actual 21.4-dBm, two-800G-channel-plus-ASE C-band load—is well supported and internally consistent. The load-bearing weakness is the extrapolation in §2A and §4: replacing the ASE-filled remainder of the C-band with additional data channels is claimed to have no impact on the quantum channel because SpRS depends only on wavelength and power, not data rate. This is asserted via refs. [26,43] but not tested in this experiment. The concern is not that SpRS is obviously data-rate-dependent; it is that the aggregate anti-Stokes noise integrated over the whole loaded C-band could depend on the power-spectral-density distribution across wavelengths if the Raman gain spectrum is not flat over the C-band, and that modulated channels could introduce modulation-dependent nonlinear effects (e.g., peak-power-dependent processes) absent from broadband ASE. The measured coexistence fidelity applies to the specific mixed ASE+two-channel population and to the total 21.4-dBm power, not automatically to 36.8 Tbps of fully data-modulated traffic. Thus the record-bandwidth and '36 Tbps without impact' claims overreach the data, even though the core coexistence demonstration is valid.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports a field demonstration of O-band polarization-entangled photon pair distribution over 24.4 km of deployed fiber between Evanston and Chicago, simultaneously with a fully-loaded C-band optical line system (OLS) carrying two 800-Gbps channels plus ASE filling (21.4 dBm aggregate launch power) and an L-band White Rabbit synchronization signal. The authors measure the SpRS spectrum generated by the broad C-band source in the O-band, select 1290 nm for the quantum signal, and use narrow spectral filtering and a 300-ps coincidence window to suppress Raman noise. They report a Bell-state fidelity of 94.2 ± 0.4% with respect to |Φ+⟩ in both dark-fiber and coexistence conditions, and a fidelity of 98.8 ± 0.1% between the coexistence and dark-fiber states. They also present a wavelength-dependent SNR and visibility simulation based on measured loss and SpRS spectra to motivate the wavelength choice. The abstract and outlook claim that the system is suitable for 36.8-Tbps classical transmission without impact on the quantum channel.","tokens_in":15300,"tokens_out":5123,"duration_ms":62219,"significance":"If the claims are fully supported, this is a notable step toward integrating entanglement-based quantum networks into real-world telecommunications infrastructure. The direct measurement of unchanged Bell-state fidelity under a realistic high-power C-band load on deployed fiber with remote synchronized nodes is a valuable experimental contribution, especially because the OLS is a commercial system with ASE-filled spectrum, rather than a single-wavelength source. The SpRS spectral data for a broadband C-band pump are also useful for wavelength planning. The paper’s strengths include the direct comparison of dark-fiber and coexistence states, the use of deployed fiber, and the characterization of synchronization timing jitter. However, the extrapolation to 36.8 Tbps rests on an untested assumption about the equivalence of ASE and data-modulated channels for SpRS generation; this overreach does not undermine the measured coexistence result but does weaken the headline capacity claim.","major_comments":[{"comment":"The statement that classical data transmission 'could be increased to 36.8 Tbps without changing the impact on the quantum system' (end of §2A) and the corresponding record-bandwidth framing in the Abstract and §4 are not directly supported by the experiment. The measured coexistence scenario uses two 800-Gbps data channels with the remainder of the C-band filled by ASE. The argument that replacing ASE with modulated data channels has no effect on SpRS is cited to refs. [26,43] but is not tested here. SpRS may depend on the power spectral density distribution across the C-band if the Raman gain spectrum is not flat, and modulated channels could introduce nonlinear effects absent from broadband ASE. A concrete remedy would be to compare the O-band SpRS spectrum or the measured fidelity when the ASE is replaced by additional data-modulated channels at the same aggregate power. Without such","section":"§2A, Eqs. (1)–(4) and Fig. 3(b)"},{"comment":"The wavelength-allocation simulation in Fig. 3(b) is presented as providing 'insights into the single channel quantum noise levels' and justifying the 1290-nm selection, but it is not an independent forward model. The simulation anchors all absolute SNR values to the measured SNR at 1290 nm and rescales the measured SpRS and loss spectra; the visibility curves are derived from the same measured quantities. As a result, the conclusion that 1260–1290 nm offers the best visibility is largely a restatement of the measured SpRS spectrum rather than a prediction validated by an independent measurement. The text should clarify that Fig. 3(b) is a scaling exercise for illustration, not a test of the wavelength-selection hypothesis.","section":"§2A, Eqs. (1)–(4), Fig. 3(b)"}],"minor_comments":[{"comment":"There are typographical errors that should be corrected: 'classsical' in the Introduction, 'nosie' in §2A, 'Univeristy' in the affiliations, and '1.6-Tpbs' in the summary paragraph. Also, 'SpRs' appears in §2B while 'SpRS' is used elsewhere; please standardize.","section":"Throughout"},{"comment":"The SpRS characterization in Fig. 3(a) was performed at 18.3-dBm launch power, while the coexistence experiment uses 21.4 dBm. The text states that the reported spectrum is normalized by launch power and later scaled, but it would be helpful to explicitly state the linear-scaling assumption and its validity in the relevant power range.","section":"§2A"},{"comment":"The description of the White Rabbit jitter measurement is clear, but the inset diagrams in Fig. 4 are small and difficult to read, particularly the distinction between the one-TDC and two-TDC configurations. A larger or simplified schematic would improve reproducibility.","section":"§2B"},{"comment":"The fidelity and visibility values are reported with Monte Carlo errors assuming Poisson statistics, but the text does not give the total coincidence counts or integration time for the tomography measurements. Reporting these (or the raw count matrices as supplementary data) would strengthen the statistical claims.","section":"§3"},{"comment":"The novelty claim 'first implementation of entanglement-based quantum communications between two remote nodes coexisting with independent classical communications traffic' should be carefully checked against ref. [48] and other recent field trials; the authors may wish to add a sentence comparing the architecture and traffic load to those works.","section":"References"}],"recommendation":"major_revision","confidential_remarks":"The core experimental result—unchanged Bell-state fidelity under a realistic 21.4-dBm C-band OLS load—is sound and well supported. The main weakness is the extrapolation to 36.8 Tbps, which relies on the equivalence of ASE and data-modulated channels for SpRS generation. This is a fixable issue: either add a measurement with additional real traffic replacing the ASE, or explicitly bound the claim to the demonstrated configuration. The authors should also clarify the scaling nature of the Fig. 3(b) simulation. If these points are addressed, the paper would be suitable for publication."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Core result is real: 94.2% Bell fidelity is unchanged when you turn on a 21.4-dBm C-band OLS and an L-band sync signal alongside a 1290-nm quantum channel over 24.4 km of installed fiber. The comparison is clean, the filtering is well motivated, and the 98.8% fidelity to the dark-fiber state makes the point directly. This is the first entanglement experiment I know of that runs against a commercial-grade fully-loaded C-band system on a deployed link between physically separated nodes, and the White Rabbit sync is a nice addition. The SpRS spectrum in the O-band and the wavelength-allocation discussion are genuinely useful for people designing hybrid networks.\n\nThe soft spots are in the extrapolation, not the measurement. The claim that replacing the ASE fill with data channels gives 36.8 Tbps 'without impact on the quantum channel' rests on the assumption that SpRS depends only on wavelength and power, not on data rate or modulation format. That is cited but not tested here. The experiment only runs two real 800G channels; the rest of the C-band is ASE. It is plausible that SpRS is data-rate independent for a given average power, but modulated channels can have peak-power effects and the Raman gain is not flat across the C-band, so the integrated anti-Stokes noise could shift. The measured coexistence fidelity applies to the actual load, not automatically to a fully data-modulated 36.8 Tbps. That should be fixed either with a direct measurement of SpRS under modulated traffic or at least by softening the language.\n\nAlso, the error bars are Monte Carlo statistical only; systematic uncertainties in filter loss, detector efficiency, and alignment are not discussed, so the fidelity may carry a hidden systematic component. The 'first implementation' claim is probably right, but it rests on the completeness of the cited literature; a comparison table would help. The Fig. 3b simulation is a rescaling of measured SpRS and loss spectra, not an independent prediction; that is fine as long as it is labeled that way, and it mostly is.\n\nOverall, the paper is worth a full review. The central demonstration is solid, and the extrapolation issue is addressable.","headline":"Solid and useful coexistence result; the measured 94.2% fidelity under a fully-loaded C-band holds up, but the 36.8 Tbps extrapolation is not tested.","tokens_in":15874,"tokens_out":1947,"would_cite":true,"duration_ms":22134,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"O-band polarization-entangled photons survive a 24.4-km fiber trip alongside 1.6 Tbps of classical traffic with unchanged Bell-state fidelity.","keywords":["quantum entanglement","wavelength-division multiplexing","coexistence","spontaneous Raman scattering","O-band","C-band","White Rabbit synchronization","deployed fiber"],"falsifier":"Replace the ASE-filled portions of the C-band with modulated 800-Gbps channels at the same aggregate power (or vary the modulation format) and re-measure the O-band SpRS counts or the |Φ+⟩ fidelity; any significant change in noise or fidelity would invalidate the data-rate-independence assumption.","tokens_in":14928,"feed_emoji":"⚛️","tokens_out":5181,"duration_ms":52772,"temperature":0.7,"pith_summary":"This paper shows that entanglement can be distributed over a real-world installed fiber link while high-power classical communications occupy the same fiber. Using O-band quantum channels at 1290/1310 nm, a fully loaded C-band classical system at 21.4 dBm, and an L-band White Rabbit synchronization signal, the authors achieve Bell-state fidelity of 94.2 ± 0.4% — identical to the dark-fiber case. They identify spontaneous Raman scattering as the main noise source and show that wavelength selection (anti-Stokes, <1300 nm) plus narrow filtering suppresses it. The result matters because it suggests quantum networks can piggyback on existing commercial fiber infrastructure without dedicated dark fiber, which is a major obstacle to scaling.","feed_headline":"Entanglement coexists with 1.6 Tbps on a real fiber","feed_subtitle":"O-band photons keep 94.2% Bell-state fidelity beside a fully loaded C-band classical line and a White Rabbit clock.","key_machinery":"The central mechanism is wavelength-division multiplexing with a large spectral gap between quantum and classical channels: the O-band quantum signal at 1290 nm sits on the anti-Stokes side of the Raman gain profile relative to the C-band classical load, where spontaneous Raman scattering is orders of magnitude weaker. Narrow Fabry-Pérot etalon filters (7-GHz FWHM), dense WDM demultiplexing (>100 dB isolation), and a 300-ps coincidence time window further reject Raman noise, while a White Rabbit optical clock at 1590 nm synchronizes the remote nodes to ~3-ps RMS jitter, enabling tight temporal filtering. This combination selects the low-noise region of the O-band spectrum (1260-1290 nm) wher","core_discovery":"The central claim is that polarization-entangled photon pairs at 1290/1310 nm can be distributed over 24.4 km of installed metropolitan fiber while coexisting with a fully-loaded C-band classical optical line system operating at 21.4 dBm aggregate launch power and an L-band optical synchronization channel, with no measurable degradation in entanglement quality. The authors report Bell-state fidelity to the |Φ+⟩ state of 94.2 ± 0.4% in both dark-fiber and coexistence configurations, and a fidelity of 98.8 ± 0.1% between the coexistence and dark-fiber states, indicating that spontaneous Raman scattering from the high-power classical channels is effectively suppressed by the chosen wavelength a","pith_inferences":["The extrapolation to 36.8 Tbps rests on the assumption that Raman noise is independent of the classical data modulation; if modulated channels generate a different Raman spectrum than ASE at the same total power, the real-world noise ceiling could be higher. A direct comparison of ASE-filled versus fully data-filled C-band would settle this.","The O-band's higher fiber loss (about 0.43 dB/km) will become more limiting at 50-100 km distances; even so, the orders-of-magnitude SpRS advantage over C-band/C-band coexistence may still favor O-band quantum channels for long-haul shared fiber.","Because the scheme relies on polarization encoding, polarization-mode dispersion and slow polarization drift on longer deployed links may require active polarization tracking; the current experiment's relatively short 24.4-km link may not reveal these effects."],"forward_implications":["Quantum networks can be deployed on the same fiber that carries commercial WDM traffic, eliminating the need for dedicated dark fiber in metropolitan links.","The demonstrated coexistence at 21.4 dBm aggregate classical power and 1.6 Tbps data rate is compatible with current telecom line systems; the authors argue the ASE-filled spectrum could carry up to 36.8 Tbps without changing the quantum noise level.","For O-band quantum channels, the paper provides a wavelength-allocation rule: channels below 1300 nm (especially 1260-1290 nm) offer the best visibility, while 1310 nm suffers roughly 6x more Raman noise.","Picosecond-level White Rabbit synchronization adds negligible timing jitter (about 3 ps RMS) relative to the 70-ps photon pulses, so remote quantum measurements can be synchronized over deployed fiber without degrading entanglement."],"fun_headline_variants":["Entanglement rides real fiber beside 1.6 Tbps classical","Quantum entanglement survives 1.6 Tbps on 24.4-km link","O-band photons keep 94% fidelity with 36-Tbps-ready C-band","First entanglement link coexisting with full C-band traffic","Entanglement and 1.6 Tbps share one fiber—94% fidelity holds"],"cache_read_input_tokens":2304,"weakest_assumption_plain":"The claim that spontaneous Raman scattering from a C-band spectrum filled with amplified spontaneous emission is identical to that from real modulated data channels, so that the measured coexistence fidelity at 1.6 Tbps represents the quantum performance at the extrapolated 36.8 Tbps.","fun_headline_variants_meta":{"raw":{"variants":["Entanglement rides real fiber beside 1.6 Tbps classical","Quantum entanglement survives 1.6 Tbps on 24.4-km link","O-band photons keep 94% fidelity with 36-Tbps-ready C-band","First entanglement link coexisting with full C-band traffic","Entanglement and 1.6 Tbps share one fiber—94% fidelity holds"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000195,"raw_usage":{"total_tokens":1198,"prompt_tokens":751,"completion_tokens":447,"prompt_tokens_details":{"cached_tokens":256},"prompt_cache_hit_tokens":256,"prompt_cache_miss_tokens":495,"completion_tokens_details":{"reasoning_tokens":348}},"tokens_in":495,"tokens_out":447,"duration_ms":5680,"temperature":1.0,"reasoning_tokens":348,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-03T06:06:27.417107+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Replace the ASE-filled portions of the C-band with modulated 800-Gbps channels at the same aggregate power (or vary the modulation format) and re-measure the O-band SpRS counts or the |Φ+⟩ fidelity; any significant change in noise or fidelity would invalidate the data-rate-independence assumption.","supporting_citations":[],"review_version":1}