{"id":"38051f2b-5853-431f-b513-170d322171ed","arxiv_id":"2606.10306","paper_version":1,"verdict":"UNVERDICTED","confidence":"LOW","novelty_score":5.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":0,"one_line_summary":"Experimental demonstration of a reconfigurable MDI-QKD/BB84 platform over 20 km fiber using EOM-generated phase-randomized weak coherent states with HOM-verified indistinguishability.","lead":"The paper shows an optical setup using a shared laser and electro-optic modulators that generates phase-randomized weak coherent states for both MDI-QKD and BB84 protocols over 20 km fiber. Reconfiguration between the two protocols requires only rotating one half-wave plate by 22.5 degrees.","discovery_kind":"new_application","skeptic_critique":{"model":"grok-4.3","headline":"Post-20 km indistinguishability of phase-randomized WCS verified only by HOM visibility ~0.5, insufficient to confirm secure partial BSM","rationale":"The reader's weakest_assumption matches the load-bearing point exactly; the abstract-only limitation is now addressed by the full text but does not resolve the verification gap. No other internal inconsistency appears in the described reconfiguration mechanism.","tokens_in":1785,"tokens_out":353,"duration_ms":25387,"concrete_test":"Recompute the expected secure key rate for the reported visibility, channel loss, and mu values using the standard MDI-QKD formula (e.g., from Lo et al. or similar); if the rate is non-positive or the visibility must exceed ~0.8 for security, perform an additional measurement of the full two-photon interference visibility under active polarization control over the 20 km link.","verdict_should_be":"CONDITIONAL","load_bearing_attack":"The central claim requires that EOM+etalon-generated mutually phase-randomized WCS remain sufficiently indistinguishable after 20 km fiber to enable secure partial BSM for MDI-QKD (and thus support the reconfigurable platform). The paper reports this via time-resolved coincidences and polarization scans yielding HOM visibility approaching the classical WCS limit of 0.5. Fiber channels introduce potential differential polarization rotation, timing jitter, or residual phase correlations not fully captured by a single HOM visibility metric; if these degrade the two-photon interference below the threshold needed for positive key rate in the security proof, the MDI-QKD mode fails even if the HWP rotation enables BB84 reconfiguration. This is load-bearing because the reconfiguration demonstration presupposes both modes function with the same transmitted states and hardware.","agreement_with_reader":"agree"},"referee_report":{"model":"grok-4.3","summary":"The manuscript demonstrates a reconfigurable optical platform supporting both polarization-encoded MDI-QKD and BB84 over 20 km fiber channels with the same hardware. Mutually phase-randomized weak coherent states are generated from a shared CW laser via EOM phase modulation and etalon sideband filtering; channel indistinguishability is verified via HOM interference (time-resolved coincidences and polarization scans) yielding visibility approaching the classical WCS limit of 0.5; partial BSM implements MDI-QKD; reconfiguration to BB84 occurs by rotating one HWP by 22.5°.","tokens_in":1952,"tokens_out":493,"duration_ms":19264,"significance":"If the post-fiber indistinguishability and reconfiguration function as described, the work offers a practical route to flexible quantum networks by eliminating protocol-specific hardware duplication. The single-laser EOM+etalon method for consistent phase-randomized WCS generation is a technical strength that could reduce complexity in dynamic environments.","major_comments":[{"comment":"Abstract: the central claim of successful MDI-QKD after 20 km requires that the reported HOM visibility (approaching 0.5) suffices for positive key rate under a security proof, yet no measured visibility value with error bars, no quantum bit error rate, and no secret key rate are provided; without these the support for secure partial BSM cannot be assessed.","section":"Abstract"},{"comment":"Abstract: fiber-induced effects (differential polarization rotation, timing jitter, residual phase correlations) are not shown to be fully captured by the single HOM metric; if these degrade two-photon interference below the threshold needed for the MDI-QKD security analysis, the reconfiguration claim (which presupposes both modes function) does not hold.","section":"Abstract"}],"minor_comments":[{"comment":"Abstract: 'sytem' is a typo for 'system'.","section":"Abstract"},{"comment":"Abstract: 'rotatinga' is missing a space; should read 'rotating a'.","section":"Abstract"},{"comment":"Abstract: '22.5 degree' should be '22.5 degrees'.","section":"Abstract"}],"recommendation":"major_revision","confidential_remarks":null},"author_rebuttal":{"model":"grok-4.3","summary":"We thank the referee for the detailed review and constructive feedback on our manuscript. We address each major comment below, focusing on clarifying the scope of our demonstration and revising the abstract accordingly.","responses":[{"response":"We agree that the abstract phrasing implies a full MDI-QKD implementation with positive key rate, which is not supported by the presented data. Our work demonstrates a reconfigurable hardware platform capable of generating mutually phase-randomized WCSs, verifies post-fiber indistinguishability via HOM, and performs partial BSM, but does not include QBER measurements or secret key rate extraction. The HOM visibility value with error bars appears in the main text (HOM interference section). We will revise the abstract to state that the platform supports MDI-QKD via partial BSM on transmitted states with verified indistinguishability, without claiming a complete key distribution experiment.","revision_made":"yes","referee_comment":"[Abstract] Abstract: the central claim of successful MDI-QKD after 20 km requires that the reported HOM visibility (approaching 0.5) suffices for positive key rate under a security proof, yet no measured visibility value with error bars, no quantum bit error rate, and no secret key rate are provided; without these the support for secure partial BSM cannot be assessed."},{"response":"The time-resolved coincidence and polarization-scan HOM measurements are performed after the 20 km fiber transmission, so the reported visibility already incorporates fiber-induced effects on the two-photon interference. We will add explicit wording in the revised abstract and/or methods to clarify this. The BB84 reconfiguration is a separate hardware adjustment (single HWP rotation) that operates independently of the MDI-QKD interference threshold; we will ensure the abstract does not overstate interdependence between the two modes.","revision_made":"yes","referee_comment":"[Abstract] Abstract: fiber-induced effects (differential polarization rotation, timing jitter, residual phase correlations) are not shown to be fully captured by the single HOM metric; if these degrade two-photon interference below the threshold needed for the MDI-QKD security analysis, the reconfiguration claim (which presupposes both modes function) does not hold."}],"tokens_in":1429,"tokens_out":470,"duration_ms":19775,"standing_objections":[]},"desk_editor":{"model":"grok-4.3","letter":"The main takeaway is that this group built and tested a setup where the same laser, EOM, etalon, and 20 km fiber channels can run either polarization MDI-QKD or BB84, switched by rotating one half-wave plate 22.5 degrees in one arm. They generate the two mutually phase-randomized weak coherent states from a single CW laser via electro-optic modulation and sideband filtering, then verify channel indistinguishability with time-resolved HOM coincidences and polarization scans that reach near the 0.5 classical limit for WCS.\n\nWhat the work actually adds is the concrete hardware-sharing demonstration. Prior MDI-QKD experiments usually need separate sources or more complex switching; here the reconfiguration is minimal and the fiber transmission is shown end-to-end. That is a practical point for anyone thinking about multi-protocol nodes in a network.\n\nThe soft spots are in the supporting numbers. The abstract states the HOM visibility approaches 0.5 but gives no value with uncertainty, no raw coincidence rates, and no extracted secret key rates or error rates for either protocol. Without those, it is hard to judge whether the two-photon interference after 20 km is actually good enough for positive key rate under the security proof, or whether residual timing jitter or polarization drift from the fiber is limiting performance. The 20 km distance is also modest for current fiber QKD work.\n\nThis paper is for experimental QKD groups and network engineers who care about reducing hardware duplication. It is worth sending to peer review so the full methods, data tables, and security analysis can be checked; the core idea is straightforward and the experiment appears honestly executed even if the headline metrics are still thin.","headline":"Reconfigurable MDI-QKD/BB84 demo over 20 km fiber with shared CW laser and single-HWP switch is a useful engineering step, but lacks reported key rates or detailed post-fiber security metrics.","tokens_in":2434,"tokens_out":428,"would_cite":false,"duration_ms":13047,"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 shared continuous-wave laser and one half-wave plate rotation let the same optical hardware run either MDI-QKD or BB84 over 20 km fiber channels.","keywords":["MDI-QKD","BB84","weak coherent states","reconfigurable quantum key distribution","Hong-Ou-Mandel interference","optical fiber channels","electro-optic modulation"],"falsifier":"A measured Hong-Ou-Mandel visibility that falls below 0.5 after 20 km transmission in a manner that prevents extraction of a positive secret key rate in the MDI-QKD configuration.","tokens_in":2703,"feed_emoji":"🔄","tokens_out":677,"duration_ms":12230,"temperature":0.7,"pith_summary":"The paper establishes that two mutually phase-randomized weak coherent states generated via electro-optic modulation and etalon filtering from one laser source can support measurement-device-independent quantum key distribution over 20 km channels, with the identical setup switched to standard BB84 by rotating a single half-wave plate 22.5 degrees in one arm. Channel indistinguishability is shown through time-resolved Hong-Ou-Mandel interference that approaches the classical limit of 0.5. A sympathetic reader would care because this removes the need for separate hardware for each protocol, cutting redundancy in quantum networks that must adapt to changing conditions.","feed_headline":"One rotation switches same hardware between MDI-QKD and BB84 over 20 km","feed_subtitle":"EOM-generated states from a shared laser allow protocol change by turning a half-wave plate 22.5 degrees without extra components.","key_machinery":"EOM-tailored weak coherent states from a shared CW laser with etalon sideband filtering, combined with partial Bell-state measurement and half-wave plate rotation for protocol switching.","core_discovery":"The central claim is that the transmitted states enable partial Bell-state measurement for MDI-QKD, while the system reconfigures directly for BB84 polarization encoding by the half-wave plate adjustment, all while preserving the same optical hardware and maintaining sufficient indistinguishability after 20 km transmission as verified by the reported interference visibility.","pith_inferences":["Networks could switch protocols on demand by remote control of the half-wave plate without physical hardware swaps.","The approach might extend to additional protocols if similar minimal adjustments preserve state indistinguishability.","Longer-distance tests would check whether the reported visibility holds over fibers beyond 20 km.","Integration with existing fiber infrastructure becomes simpler if the shared-laser source can serve multiple nodes."],"forward_implications":["MDI-QKD proceeds directly from the partial Bell-state measurement on the transmitted states.","BB84 operates on the same hardware after the 22.5-degree half-wave plate rotation without other changes.","Hardware redundancy drops because one module handles both protocols.","Operational flexibility increases for dynamic network environments.","EOM-based frequency engineering from a shared laser provides a practical route to scalable quantum communication."],"fun_headline_variants":["22.5 degree HWP rotation reconfigures MDI-QKD to BB84 over 20 km","EOM and etalon produce WCSs for reconfigurable MDI-QKD and BB84 on 20 km fiber","Partial BSM with WCSs supports MDI-QKD to BB84 switch via HWP over 20 km","Shared CW laser enables 20 km channel MDI-QKD and BB84 with EOM WCSs"],"cache_read_input_tokens":2112,"weakest_assumption_plain":"The two phase-randomized weak coherent states remain sufficiently indistinguishable after 20 km fiber transmission for secure partial Bell-state measurement to function.","fun_headline_variants_meta":{"raw":{"variants":["22.5 degree HWP rotation reconfigures MDI-QKD to BB84 over 20 km","EOM and etalon produce WCSs for reconfigurable MDI-QKD and BB84 on 20 km fiber","Partial BSM with WCSs supports MDI-QKD to BB84 switch via HWP over 20 km","Shared CW laser enables 20 km channel MDI-QKD and BB84 with EOM WCSs"]},"model":"grok-4.3","cost_usd":0.006475,"raw_usage":{"total_tokens":3053,"prompt_tokens":711,"num_sources_used":0,"completion_tokens":110,"cost_in_usd_ticks":64749500,"prompt_tokens_details":{"text_tokens":711,"audio_tokens":0,"image_tokens":0,"cached_tokens":256},"completion_tokens_details":{"audio_tokens":0,"reasoning_tokens":2232,"accepted_prediction_tokens":0,"rejected_prediction_tokens":0}},"tokens_in":711,"tokens_out":110,"duration_ms":14759,"temperature":1.0,"reasoning_tokens":2232,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-06-27T13:19:32.508223+00:00","model_set":{"reader":"grok-4.3"},"falsifier":"A measured Hong-Ou-Mandel visibility that falls below 0.5 after 20 km transmission in a manner that prevents extraction of a positive secret key rate in the MDI-QKD configuration.","supporting_citations":[],"review_version":1}