{"id":"03ea6b14-9e11-4941-b022-c1ecb3ec513e","arxiv_id":"2412.07798","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":0,"one_line_summary":"Cavity-enhanced measurements show broadband spin-dependent optical absorption from NV centers from 710 to 1000 nm, yielding ODMR contrasts up to 42% and a photon-shot-noise-limited sensitivity of 7.5 pT/√Hz at 960 nm.","lead":"The paper shows that nitrogen-vacancy centers in diamond absorb light across a broad red-to-infrared range, and this absorption can be used to detect magnetic fields with much higher contrast than typical fluorescence readout. This opens a new wavelength window for compact, sensitive magnetometers and could help build laser-based quantum sensors.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The abstract's 'broadband optical absorption starting in the emission wavelength' conflates stimulated emission at short probe wavelengths with true absorption; the absorption band's onset is not established.","rationale":"I read the paper as claiming a new absorption phenomenon over a wide wavelength range. The strongest evidence for NV involvement is the ODMR resonance structure, which convincingly fingerprints the NV spin transition. However, the paper itself discloses in §3.1 that at low probe wavelengths the contrast arises from stimulated emission, not absorption. This means the absorption claim's spectral boundaries are unverified. The reader's concern about PSNL sensitivity is valid but secondary because the paper explicitly labels the sensitivity as photon-shot-noise-limited. My proposed test would determine the absorption onset and thus settle whether the abstract's central claim is accurate. If the crossover is around 800 nm, the paper remains publishable with revised wording, so I recommend no change to the reader's CONDITIONAL verdict.","tokens_in":10153,"tokens_out":18972,"duration_ms":201440,"concrete_test":"Compute the per-pass gain/loss change on MW resonance for each probe wavelength from the finesse and ODMR contrast data in Fig. 2 and Supplement S2, using the cavity relation C ≈ Δ(loss)/total_loss. Compare the wavelength dependence to the known NV stimulated emission spectrum [27] and the 1E singlet absorption spectrum [33]. Fit a two-component model (emission gain plus absorption loss) to the contrast-vs-wavelength data and extract the crossover wavelength λ_x where absorption dominates. If λ_x is significantly above 710 nm, revise the abstract and title to specify that the absorption band extends from λ_x to 1000 nm, rather than 'starting in the emission wavelength'.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim in the abstract is 'a phenomenon of broadband optical absorption by the NV centers starting in the emission wavelength and reaching up to 1000 nm.' However, §3.1 states that 'for small probe wavelengths the high contrast can well be explained by magnetic-field-dependent stimulated emission of the NV centers into the cavity mode [27]' and only 'at high probe wavelengths' does 'a broadband microwave-induced optical absorption' become the reason. Thus the ODMR signals at 710 nm and other short wavelengths are likely dominated by the already-known stimulated emission, not by the new absorption. The paper never measures the crossover wavelength at which absorption begins to dominate, nor does it separate the emission and absorption contributions spectrally. If the absorption band actually starts around 800 nm rather than at the emission wavelength, the abstract's claim is overstated and the title's 'absorption magnetometry in the visible range' is misleading. Because the paper's novelty rests on the spectral extent of the absorption, this unquantified conflation is the most load-bearing weakness.","agreement_with_reader":"disagree"},"referee_report":{"model":"deepseek-v4-flash","summary":"This manuscript reports cavity-enhanced continuous-wave pump-probe ODMR measurements on a 1.9 ppm NV ensemble in diamond, with a probe laser tunable between 710 nm and 1000 nm. The authors observe spin-resonant changes in cavity transmission with ODMR contrasts up to 42%, increasing with probe wavelength, and attribute the long-wavelength signals to a broadband microwave-induced optical absorption whose lower level is tentatively the 1E singlet state. By iterating pump and microwave powers at each wavelength they report an optimized photon-shot-noise-limited sensitivity of 7.5 pT/√Hz at 960 nm, and argue that this opens a new detection wavelength regime for NV magnetometry.","tokens_in":10322,"tokens_out":5205,"duration_ms":53535,"significance":"If the interpretation is correct, the paper makes a useful experimental advance: it demonstrates spin-dependent absorption signals at wavelengths where NV emission is negligible, with record-level ODMR contrast and coherent (mW-level) detection, and it provides quantitative evidence relevant to laser-threshold magnetometry at red/IR wavelengths. The strengths include direct measurements of contrast, linewidth, and cavity signal, a standard PSNL formula with no fitted parameter in the central claim, and consistency checks against the known singlet absorption spectrum [33]. The main caveats are that the reported sensitivity is a photon-shot-noise limit rather than a measured noise floor, and that the spectral boundary between stimulated emission and true absorption is not measured; both are explicitly or implicitly acknowledged in the manuscript, but they affect how the headline claims should be framed.","major_comments":[{"comment":"The abstract states 'broadband optical absorption by the NV centers starting in the emission wavelength', but §3.1 says that at small probe wavelengths the high contrast 'can well be explained by magnetic-field-dependent stimulated emission' and that only at high probe wavelengths does 'a broadband microwave-induced optical absorption' become the reason. The crossover wavelength at which absorption begins to dominate is not measured and the two contributions are not separated spectrally. Since the claimed novelty is the spectral extent of the absorption, the paper should either restrict the absorption claim to the wavelength range where it is actually supported, or provide a quantitative separation (e.g., power/linewidth dependence that distinguishes gain from loss). This is the main load-bearing issue.","section":"Abstract and §3.1"},{"comment":"The headline sensitivity of 7.5 pT/√Hz is a photon-shot-noise-limited estimate computed from η ∝ δν/(C√R), not a measured noise floor. This is made clear in some places (e.g., the final section states that technical noise will be studied in the future), but the abstract and Fig. 4 present it as 'the best PSNL sensitivity' without the qualifier 'estimated' or 'projected'. Because technical noise (cavity-length jitter, laser intensity noise, microwave inhomogeneity) could easily dominate the quoted value, the manuscript should consistently label all such values as calculated PSNL limits and, if possible, report a measured Allan deviation or noise spectrum.","section":"§3.2 and §4"}],"minor_comments":[{"comment":"'starting in the emission wavelength' should be 'starting within the emission band' or 'starting at 710 nm'; the current phrasing is grammatically ambiguous and, in view of the stimulated-emission contribution, potentially misleading.","section":"Abstract"},{"comment":"'The Δ symbolizes theindividualpower,beamsizeandpolarizationadjustments' contains missing spaces and should be reworded.","section":"Section 2"},{"comment":"'The data is fitted with a double Lorentzian' should be 'The data are fitted with a double Lorentzian'.","section":"§3.1"},{"comment":"'two neighboring measurements points' should be 'two neighboring measurement points'.","section":"Fig. 2(c) caption"},{"comment":"The statement that the contrast is 'a new record for an ensemble of NV centers' would benefit from a citation or a clear definition of the comparison set.","section":"§3.1"},{"comment":"Please verify the volume/page details for Ref. 18 ('Phys. Rev. Lett. 5') and Ref. 8 ('nature7'); as printed they are incomplete.","section":"References"}],"recommendation":"major_revision","confidential_remarks":"The paper is within the scope of physics.app-ph and the experimental work appears genuine and carefully carried out. My recommendation is driven by framing: the abstract and title overstate the spectral extent of the absorption, and the sensitivity headline needs an 'estimated' qualifier. Both are fixable with revisions. I do not see circularity or fitted-parameter concerns; the central PSNL number is computed from a standard formula."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Colleague,\n\nThe paper deserves a serious referee, but it needs a revision before acceptance. What's actually new: the authors show cavity-enhanced cw pump-probe ODMR from 710 nm to 1000 nm with contrasts up to 42% total at 1000 nm, and a sensitivity-optimization curve peaking at 7.5 pT/√Hz (shot-noise-limited, calculated) at 960 nm. The high-wavelength signals—where spontaneous emission is negligible—are a genuine demonstration of broadband microwave-induced absorption by an NV ensemble at room temperature, extending prior single-wavelength off-resonant work at 912 nm. The finesse data and the qualitative match to the known singlet absorption spectrum [33] make the absorption interpretation credible.\n\nCredit where due: the paper is careful in Section 3.1 to say that the short-wavelength contrast is well explained by the group's earlier stimulated-emission mechanism, and that absorption takes over at high wavelengths. It doesn't hide that the singlet assignment is an argument, not a proof. And the LPHT-treated diamond giving high finesse over this band is a real technical achievement.\n\nThe soft spots are proportionate. First, the abstract and title say 'broadband optical absorption starting in the emission wavelength,' which is misleading: at 710–750 nm the ODMR is dominated by stimulated emission, not absorption, and the crossover is never measured. That needs to be fixed or the claim softened. Second, the 7.5 pT/√Hz is a photon-shot-noise limit from the standard formula, not a measured noise floor; the authors acknowledge technical noise is future work, but the plot and abstract should keep that distinction visible. Third, no error bars on the headline contrast or sensitivity values. The supplement might have them, but the main text gives none. Fourth, the lower-singlet assignment is plausible and consistent with [33], but other states (e.g., charge-state effects) aren't ruled out. The paper says 'could be'—good—but a reviewer should ask for a more direct test or a clear statement that it's a hypothesis.\n\nThe central phenomenon holds up, and the issues are fixable with rewording plus a few numbers. The citation pattern looks fair, and the authors correctly build on their own earlier work and on Kehayias et al. This is a solid contribution to cavity-enhanced quantum sensing, not a field-reshaping one. I'd send it to peer review and ask for those revisions. A reader focused on NV magnetometry or LTM will get value from it.\n\nBest,\n[your name]","headline":"Broadband absorption ODMR out to 1000 nm is real and useful, but the abstract oversells the visible-range part and the headline sensitivity is a shot-noise estimate, not a measured floor.","tokens_in":10874,"tokens_out":2271,"would_cite":true,"duration_ms":23731,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"This paper demonstrates that nitrogen-vacancy centers in diamond absorb light across a broad band from 710 nm to 1000 nm in a spin-dependent way, enabling cavity-enhanced absorption magnetometry with ODMR contrasts up to 42% and a…","keywords":["nitrogen-vacancy centers","magnetometry","cavity-enhanced spectroscopy","optically detected magnetic resonance","singlet-state absorption","photon-shot-noise-limited sensitivity","diamond quantum sensing","near-infrared absorption"],"falsifier":"Lock the cavity at the 960 nm operating point and record the actual magnetic-field noise spectral density; if the measured noise floor is significantly above 7.5 pT/√Hz after removing technical noise, the reported sensitivity overstates practical performance.","tokens_in":1746,"feed_emoji":"💎","tokens_out":8070,"duration_ms":152232,"temperature":0.7,"pith_summary":"Nitrogen-vacancy (NV) centers in diamond are usually read out by their red fluorescence or by absorption at the single 1042 nm singlet transition. This paper shows a third readout: a broadband, spin-dependent optical absorption that starts in the emission band and extends to 1000 nm, observed at room temperature with a high-finesse optical cavity. The probe beam passes through the diamond hundreds of times, and the resulting optically detected magnetic resonance (ODMR) signals reach contrasts up to 42%—much higher than fluorescence-based readout. The authors identify the likely absorber as the lower NV singlet state, populated by resonant microwaves, and estimate a photon-shot-noise-limited sensitivity of 7.5 pT/$\\sqrt{\\mathrm{Hz}}$ at 960 nm. If the result holds, NV magnetometers could use bright coherent lasers in the red-to-NIR range as the signal carrier, a new wavelength regime for this sensor.","feed_headline":"NV magnetometry gains a red-to-NIR readout with 42% contrast","feed_subtitle":"A high-finesse cavity turns broadband NV absorption into shot-noise-limited sensing at 7.5 pT/√Hz.","key_machinery":"The central mechanism is a high-finesse linear optical cavity ($F > 1200$) containing a diamond placed at Brewster's angle, so the probe laser makes many round trips through the NV ensemble and the effective absorption length grows by a factor $N = 2F/\\pi \\approx 450$. A resonant microwave field increases the population of the lower singlet state $^{1}E$, which then absorbs the probe light off-resonantly across a broad red-to-NIR band; the resulting transmission dip is the ODMR signal. The same cavity also enhances stimulated emission near 710 nm, and the authors attribute the rising contrast toward 1000 nm to the wavelength-dependent absorption of the lower singlet state, whose broad spectrum they cite from earlier measurements.","core_discovery":"At room temperature, the authors place a diamond containing roughly 1.9 ppm NV$^-$ centers in a high-finesse cavity, pump it at 532 nm, and send a tunable 710–1000 nm probe beam through the cavity. They observe an optically detected magnetic resonance (ODMR) signal at every probe wavelength: when a resonant microwave field is applied, the transmitted probe power drops because the diamond absorbs more light. The contrast grows with wavelength, from a few percent near 710 nm to more than 32% for a single spin resonance (and 42% total) at 1000 nm. Because spontaneous and stimulated emission are negligible at the long-wavelength end, the paper argues the absorption is an off-resonant transition from the lower NV singlet state $^{1}E$, whose population is increased by resonant microwave driving. Optimizing pump and microwave power at 960 nm yields an estimated photon-shot-noise-limited sensitivity of 7.5 pT/$\\sqrt{\\mathrm{Hz}}$ with a dynamic range of about 280 µT.","pith_inferences":["If the lower-singlet assignment is correct, the same cavity technique becomes a room-temperature spectrometer for the NV singlet absorption band, potentially mapping its full lineshape between 700 and 1042 nm with ODMR contrast as the readout.","The sensitivity trend with wavelength implies that moving the probe closer to the 1042 nm singlet resonance, or increasing probe power near 1000 nm beyond the available laser limit, could push the photon-shot-noise limit below 7.5 pT/√Hz.","The strong pump-induced absorption at longer wavelengths suggests an operating trade-off the paper does not fully resolve: higher pump power improves spin polarization but also loads the cavity with extra loss, so pulsed or spatially separated pump and probe geometries might improve the achievable finesse and contrast.","A direct measurement of the locked-cavity noise floor would tell whether the 7.5 pT/√Hz estimate survives technical noise; without it, the practical device sensitivity remains an open question."],"forward_implications":["Magnetometry with NV ensembles can be read out with a bright coherent probe from 710 to 1000 nm, not only with fluorescence or the resonant 1042 nm singlet transition.","ODMR contrast increases continuously with probe wavelength in this range, reaching split-resonance contrasts above 32% and total contrast above 42% at 1000 nm.","The optimized photon-shot-noise-limited sensitivity improves with wavelength, reaching 7.5 pT/$\\sqrt{\\mathrm{Hz}}$ at 960 nm with a dynamic range near 280 µT.","The same broadband absorption enables room-temperature spectroscopy of the NV singlet band across wavelengths that were previously inaccessible.","These results support efforts toward laser threshold magnetometry at higher red and infrared wavelengths, where the contrast boost is largest."],"supporting_citations":[{"why":"Provides the prior demonstration of 17% ODMR contrast via stimulated emission at 710 nm and the cavity setup this work extends.","marker":"[27]"},{"why":"Supplies the multi-pass enhancement factor $N = 2F/\\pi$ used to amplify the weak singlet absorption.","marker":"[30]"},{"why":"Gives the 1042 nm cavity-enhanced absorption magnetometry baseline whose sensitivity is improved by a factor of three here.","marker":"[31]"},{"why":"Supplies the earlier scheme for spin readout through infrared absorption at the NV singlet transition.","marker":"[32]"},{"why":"Provides the measured absorption spectrum and vibronic sidebands of the lower singlet state used to argue the off-resonant absorption.","marker":"[33]"},{"why":"Supplies the temperature dependence of the singlet absorption that explains why the effect requires a multi-pass cavity at room temperature.","marker":"[34]"},{"why":"Documents the diamond pretreatment that reduces broadband absorption and enables the high cavity finesse.","marker":"[36]"}],"fun_headline_variants":["NV absorption magnetometry: 42% contrast, 7.5 pT/√Hz","Broadband NV absorption enables high-contrast sensing","Red-to-NIR NV magnetometry with cavity boost","NV spin readout via absorption up to 1000 nm","High-finesse cavity turns NV absorption into magnetometry"],"cache_read_input_tokens":13056,"weakest_assumption_plain":"The headline sensitivity is a photon-shot-noise-limited estimate, not a measured noise floor; it rests on the assumption that technical noise from cavity-length jitter, laser intensity noise, and microwave inhomogeneity is negligible.","fun_headline_variants_meta":{"raw":{"variants":["NV absorption magnetometry: 42% contrast, 7.5 pT/√Hz","Broadband NV absorption enables high-contrast sensing","Red-to-NIR NV magnetometry with cavity boost","NV spin readout via absorption up to 1000 nm","High-finesse cavity turns NV absorption into magnetometry"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000708,"raw_usage":{"total_tokens":3209,"prompt_tokens":987,"completion_tokens":2222,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":603,"completion_tokens_details":{"reasoning_tokens":2134}},"tokens_in":603,"tokens_out":2222,"duration_ms":16826,"temperature":1.0,"reasoning_tokens":2134,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-11T21:07:19.783138+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Lock the cavity at the 960 nm operating point and record the actual magnetic-field noise spectral density; if the measured noise floor is significantly above 7.5 pT/√Hz after removing technical noise, the reported sensitivity overstates practical performance.","supporting_citations":[{"cited_title":"Magnetic-field-dependantstimulatedemissionfromnitrogen-vacancycenters in diamond,","cited_arxiv_id":null,"evidence_quote":"Provides the prior demonstration of 17% ODMR contrast via stimulated emission at 710 nm and the cavity setup this work extends."},{"cited_title":"Cavity-enhanced room-temperature magnetometry using absorption by nitrogen-vacancy centers in diamond,","cited_arxiv_id":null,"evidence_quote":"Supplies the multi-pass enhancement factor $N = 2F/\\pi$ used to amplify the weak singlet absorption."},{"cited_title":"Miniature cavity-enhanced diamond magnetometer,","cited_arxiv_id":null,"evidence_quote":"Gives the 1042 nm cavity-enhanced absorption magnetometry baseline whose sensitivity is improved by a factor of three here."},{"cited_title":"Magnetometry with nitrogen-vacancy ensembles in diamond based on infrared absorption in a doubly resonant optical cavity,","cited_arxiv_id":null,"evidence_quote":"Supplies the earlier scheme for spin readout through infrared absorption at the NV singlet transition."},{"cited_title":"Infraredabsorptionbandandvibronicstructureofthenitrogen-vacancy center in diamond,","cited_arxiv_id":null,"evidence_quote":"Provides the measured absorption spectrum and vibronic sidebands of the lower singlet state used to argue the off-resonant absorption."},{"cited_title":"Supplemenatry materials to: Infrared absorption band and vibronic structure of the nitrogen-vacancy center in diamond,","cited_arxiv_id":null,"evidence_quote":"Supplies the temperature dependence of the singlet absorption that explains why the effect requires a multi-pass cavity at room temperature."},{"cited_title":"Cavity-enhanced magnetic-field sensing via stimulated emission from nitrogen-vacancy centres in diamond,","cited_arxiv_id":null,"evidence_quote":"Documents the diamond pretreatment that reduces broadband absorption and enables the high cavity finesse."}],"review_version":1}