{"id":"6689bb2f-7b53-4043-805b-f133e6aae821","arxiv_id":"2606.17365","paper_version":1,"verdict":"CONDITIONAL","confidence":"LOW","novelty_score":6.0,"correctness_risk":"low","formal_verification":"none","parameter_count":0,"one_line_summary":"A receiver-level framework for time-spectral control of accidental coincidences enables practical daylight operation of entanglement-based free-space BBM92 QKD with quantified design margins.","lead":"The paper develops a receiver framework linking bandwidth, temporal window, and background density to key rates and errors in daylight entanglement QKD. It validates the approach with indoor parameter sweeps and a 10 m rooftop test achieving 2811 cps sifted rate at 4.43% QBER.","discovery_kind":"new_method","skeptic_critique":{"model":"grok-4.3","headline":"Framework assumes accidental coincidences arise solely from Poissonian random temporal overlaps between signal and background photons, with no significant dark-count, multi-photon, or spatial-mode contributions.","rationale":"The reader's weakest_assumption correctly isolates the modeling step whose violation would directly invalidate the derived rates and the daylight validation; no other internal inconsistency appears in the abstract-level claim.","tokens_in":1709,"tokens_out":304,"duration_ms":26111,"concrete_test":"Independently measure the detector dark-count rate (gated, same bias and temperature) and subtract it from the reported Bob singles; recompute the model-predicted accidental fraction using only the residual singles and compare to the observed QBER—if the residual after subtraction deviates from the Poisson term by >15 % of the reported uncertainty, the assumption fails.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The receiver-level framework derives closed-form links from bandwidth, temporal width, and background density to Bob singles, sifted rate, error rate, and QBER under the Poisson-overlap model alone. If detector dark counts (even at typical InGaAs levels) or residual multi-photon probability from the entangled source add non-negligible accidentals, the predicted saturation behavior, temporal-window margin contraction, and 4.43 % QBER in the rooftop run would systematically under-estimate contamination; the design map and claim of “predicted low-accidental regime” would then rest on an incomplete noise budget.","agreement_with_reader":"agree"},"referee_report":{"model":"grok-4.3","summary":"The manuscript develops and experimentally validates a receiver-level framework that connects receiver bandwidth, accepted temporal width, and background-noise density to Bob singles rate, sifted-key rate, error rate, and QBER for telecom-wavelength BBM92 entanglement-based QKD. Indoor sweeps demonstrate saturation of useful sifted counts near source-matched bandwidth and increased accidental contamination with broader bandwidth or higher background; a two-dimensional design map illustrates contraction of temporal-window margin with rising background-to-signal ratio. A 10 m rooftop daylight experiment reports a mean sifted-key rate of 2,811 cps and mean QBER of 4.43% in the predicted low-accidental regime.","tokens_in":1838,"tokens_out":498,"duration_ms":21491,"significance":"If the framework holds under the stated noise model, it supplies a concrete, closed-form design tool for time-spectral filtering that directly predicts how parameter choices affect key rates and QBER in daylight free-space QKD, a regime where background light is the dominant limitation. The rooftop demonstration supplies concrete performance numbers (2811 cps, 4.43 % QBER) obtained under real daylight conditions, and the validation against measured external rates rather than internal fits adds credibility to the Poisson-overlap model.","major_comments":[{"comment":"Abstract and the paragraph describing the receiver-level framework: the derivation assumes accidental coincidences arise solely from Poissonian random temporal overlaps between signal and background photons. The manuscript should explicitly quantify or bound the contributions of InGaAs detector dark counts, residual multi-photon probability from the entangled source, and spatial-mode mismatch under the experimental conditions; if these are non-negligible they would systematically alter the predicted saturation behavior and the claimed low-accidental regime.","section":"receiver-level framework (abstract)"}],"minor_comments":[{"comment":"The abstract states that full data tables and error analysis are referenced but not shown; the main text should include tabulated raw counts, uncertainty propagation, and goodness-of-fit metrics for the indoor sweeps so that the saturation and QBER trends can be independently verified.","section":"results section"},{"comment":"Figure captions for the design map should explicitly label the axes in terms of background-to-signal ratio and state the source parameters used to generate the curves.","section":"design map figure"}],"recommendation":"major_revision","confidential_remarks":null},"author_rebuttal":{"model":"grok-4.3","summary":"We thank the referee for the constructive feedback and positive assessment of the framework. We address the single major comment below.","responses":[{"response":"We agree that explicit bounds improve clarity. Section II derives the framework under the standard Poisson-overlap model for background photons, the dominant term in daylight. InGaAs dark-count rates are measured at <50 cps per detector under operating conditions, negligible relative to background singles (>10^4 cps). The SPDC source multi-photon probability is bounded by g^(2)(0)<0.05, yielding <1% multi-pair contribution within the coincidence window. Spatial-mode mismatch is incorporated via measured system efficiency and visibility (>92% rooftop), producing no additional accidental term beyond the temporal model. These contributions remain negligible and preserve the reported saturation behavior and low-accidental regime. We will add a dedicated paragraph with these bounds in the revised Section III.","revision_made":"yes","referee_comment":"[receiver-level framework (abstract)] Abstract and the paragraph describing the receiver-level framework: the derivation assumes accidental coincidences arise solely from Poissonian random temporal overlaps between signal and background photons. The manuscript should explicitly quantify or bound the contributions of InGaAs detector dark counts, residual multi-photon probability from the entangled source, and spatial-mode mismatch under the experimental conditions; if these are non-negligible they would systematically alter the predicted saturation behavior and the claimed low-accidental regime."}],"tokens_in":1340,"tokens_out":311,"duration_ms":28371,"standing_objections":[]},"desk_editor":{"model":"grok-4.3","letter":"This paper gives a receiver-level framework that ties bandwidth, temporal window, and background density to the key QKD performance numbers in daylight telecom BBM92. The two-dimensional design map and the rooftop validation are the parts worth paying attention to.\n\nThey show that sifted counts level off once the receiver bandwidth matches the source, while extra bandwidth or background mainly pumps up accidentals. Widening the time window does almost nothing to the singles rate but steadily raises QBER through more random overlaps. The map makes clear that the safe temporal margin shrinks quickly as background rises, but the bandwidth choice has more room near the matched point. The 10 m daylight test delivered 2811 cps sifted key at 4.43 % QBER, which sits in the regime their model flags as low-accidental.\n\nThe derivation uses ordinary Poisson arrival statistics and checks against external measured rates rather than internal fits, so the circularity risk stays low. The indoor sweeps supply the concrete numbers that back the saturation behavior.\n\nThe main limitation is the noise model. It treats accidentals as coming only from signal-background overlaps under Poisson statistics. Typical InGaAs dark counts or any leftover multi-photon probability from the entangled pair source could add extra contamination that the map does not capture. If those terms are not negligible, the predicted margins and the claim of operating in the low-accidental regime would need adjustment. The abstract does not show the full noise breakdown, so that check belongs in the complete manuscript.\n\nGroups working on outdoor QKD hardware will find the design map directly usable for setting receiver parameters. The experimental results are specific enough that a referee can evaluate whether the model holds once the other noise sources are quantified. I would send it to peer review.","headline":"Receiver design map for daylight QKD with experimental checks, but noise budget needs full verification.","tokens_in":2322,"tokens_out":416,"would_cite":true,"duration_ms":28205,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"grok-4.3","headline":"A receiver framework links bandwidth and time window to reduced accidental coincidences in daylight QKD.","keywords":["quantum key distribution","entanglement","daylight operation","accidental coincidences","receiver bandwidth","temporal window","free-space QKD"],"falsifier":"Measuring QBER and sifted rate while varying background density at fixed bandwidth and time window; if the observed values deviate significantly from the framework's predictions, the model would be falsified.","tokens_in":2611,"feed_emoji":"📡","tokens_out":633,"duration_ms":32822,"temperature":0.7,"pith_summary":"The paper develops and tests a model that connects a QKD receiver's bandwidth, its accepted time window, and the density of background light to the rate of detected photons, the sifted key rate, and the error rate in an entanglement-based system. A sympathetic reader would care because daylight QKD is hampered by bright background light creating false coincidences that raise errors and waste key bits. By showing that matching the bandwidth to the source and keeping the time window narrow keeps the system in a low-error regime, the work points to practical parameter choices for outdoor links. Indoor measurements confirm that sifted rates plateau once bandwidth matches the source, while wider settings mainly add noise. A rooftop test in daylight achieves 2811 cps sifted rate at 4.43 percent QBER when operated in the predicted regime.","feed_headline":"Tuning bandwidth and time window cuts QKD noise in daylight","feed_subtitle":"A model shows how matching receiver settings to the photon source keeps accidental overlaps low enough for reliable key rates outdoors.","key_machinery":"The receiver-level framework that models accidental coincidences as arising from random temporal overlaps under Poisson statistics between signal and background photons.","core_discovery":"The central claim is that accidental coincidences in daylight entanglement-based free-space QKD can be controlled at the receiver by tuning bandwidth and temporal acceptance width, with a validated framework that predicts Bob singles, sifted-key rate, error rate, and QBER from receiver bandwidth, temporal width, and background-noise density in telecom-wavelength BBM92 QKD.","pith_inferences":["Similar tuning could extend to other free-space QKD setups with different wavelengths or protocols.","The design map suggests adaptive receivers that adjust time window based on real-time background measurements.","Extending the model to include spatial filtering effects might further improve performance in turbulent conditions."],"forward_implications":["Useful sifted counts saturate near the source-matched bandwidth.","Broader bandwidth or higher background mainly increases accidental contamination.","Increasing the accepted temporal width raises QBER by enlarging random-overlap probability.","The temporal-window margin contracts rapidly with increasing background-to-signal ratio while bandwidth margin stays broad near source-matched filtering."],"fun_headline_variants":["Bandwidth tuning reduces accidental coincidences in daylight QKD","Temporal acceptance width controls QBER in daylight QKD","Validated model predicts QKD rates from receiver bandwidth","Two-dimensional map guides low-accidental daylight QKD"],"cache_read_input_tokens":2112,"weakest_assumption_plain":"Accidental coincidences arise solely from random temporal overlaps between signal and background photons under Poisson statistics.","fun_headline_variants_meta":{"raw":{"variants":["Bandwidth tuning reduces accidental coincidences in daylight QKD","Temporal acceptance width controls QBER in daylight QKD","Validated model predicts QKD rates from receiver bandwidth","Two-dimensional map guides low-accidental daylight QKD"]},"model":"grok-4.3","cost_usd":0.00524,"raw_usage":{"total_tokens":2514,"prompt_tokens":621,"num_sources_used":0,"completion_tokens":60,"cost_in_usd_ticks":52399500,"prompt_tokens_details":{"text_tokens":621,"audio_tokens":0,"image_tokens":0,"cached_tokens":256},"completion_tokens_details":{"audio_tokens":0,"reasoning_tokens":1833,"accepted_prediction_tokens":0,"rejected_prediction_tokens":0}},"tokens_in":621,"tokens_out":60,"duration_ms":22874,"temperature":1.0,"reasoning_tokens":1833,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-06-27T02:40:01.971055+00:00","model_set":{"reader":"grok-4.3"},"falsifier":"Measuring QBER and sifted rate while varying background density at fixed bandwidth and time window; if the observed values deviate significantly from the framework's predictions, the model would be falsified.","supporting_citations":[],"review_version":1}