Atlas of the Present Atlas · v0.1

As of 12 September 2026

Dossier 05

Quantum Sensing

v1.2-draft · unchecked

1. As of

Date
Version
v1.2-draft
Author / model
Atlas generator
Reviewer
unchecked (Josef)

2. In one sentence

Quantum sensing is already deployed as Cs fountains, GPS rubidium, and SERF OPMs in shielded rooms; Budker/Romalis (2007 review, arXiv) set SERF sensitivity >10⁻¹⁵ T/√Hz and near-zero-field <~10 nT; optical record clocks including Bothwell (E1) and atom gravimeters are lab/hybrid — not backpack 10⁻¹⁸ chronometers and not an ESA quantum satellite in 2026.

Established now · E1 / E2

3. What works today

What quantum sensing is — Type I/II deployed, Type III not

  1. E1

    Degen: (I) a quantized object as the probe, (II) coherence/superposition, (III) entanglement beyond the classical limit. Historical examples: SQUID, atomic-vapour magnetometers, atomic clocks. Type I/II often close to applications; Type III is the strict definition. Atomic clocks are explicitly excluded in the review — clock figures come from NIST/Marshall, not Degen.

    Degen, Reinhard, Cappellaro. Quantum sensing. https://arxiv.org/html/1611.02427. As of 2017-06. Checked 2026-08-28. Type: Review (RMP 89).

Atomic clocks: Cs defines the second; optical clocks are laboratory

  1. E1

    The SI second is 9,192,631,770 periods of the Cs-133 hyperfine transition. UTC(NIST) from maser+beam, calibrated by fountains. Optical clocks contribute but are not primary standards, “because the second is currently defined in terms of cesium.”

    NIST How Do We Know. How Do We Know What Time It Is?. https://www.nist.gov/atomic-clocks/how-do-we-know-what-time-it. As of 2025-05-28. Checked 2026-08-28. Type: Agency.NIST Fountain page. NIST’s Cesium Fountain Atomic Clocks. https://www.nist.gov/pml/time-and-frequency-division/time-realization/cesium-fountain-atomic-clocks. As of 2023-05-12. Checked 2026-08-28. Type: Agency.
  2. E2

    NIST-F4: type-B uncertainty 2.2×10⁻¹⁶ (abstract + news; body not opened). Fountains “very delicate”; <20 worldwide. F3+F4 ~90% uptime.

    NIST F4 News. New Atomic Fountain Clock Joins Elite Group That Keeps the World on Time. https://www.nist.gov/news-events/news/2025/04/new-atomic-fountain-clock-joins-elite-group-keeps-world-time. As of 2025-04-28. Checked 2026-08-28. Type: Agency.
  3. E1

    ²⁷Al⁺ quantum-logic clock: systematic uncertainty 5.5×10⁻¹⁹; instability 3.5×10⁻¹⁶/√(τ/s). 1 s probe via 3.6 km fibre to JILA’s cryogenic Si cavity. This is a metrology campus, not a field device.

    Marshall et al. High-stability single-ion clock with 5.5×10⁻¹⁹ systematic uncertainty. https://arxiv.org/html/2504.13071v1. As of 2025-04. Checked 2026-08-28. Type: Paper (PRL 135).NIST Ion Clock News. NIST Ion Clock Sets New Record for Most Accurate Clock in the World. https://www.nist.gov/news-events/news/2025/07/nist-ion-clock-sets-new-record-most-accurate-clock-world. As of 2025-07-14. Checked 2026-08-28. Type: Agency.
  4. E1

    BACON 2025: Al⁺/Sr, Al⁺/Yb, Yb/Sr uncertainties 2.2 / 3.2 / 3.1 ×10⁻¹⁸. Al⁺/Sr deviates ~14σ from BACON21; repeatability <10⁻¹⁷ remains an “outstanding issue” (authors). E3 for “milestone for redefinition” (Dimarcq not opened).

    Aeppli / BACON. Atomic clock frequency ratios with fractional uncertainty ≤3.2×10⁻¹⁸. https://arxiv.org/html/2512.21428v1. As of 2025-12. Checked 2026-08-28. Type: Paper.
  5. E1

    GPS: 31 satellites, rubidium clocks only onboard today; drift around a few nanoseconds per day; steered by ground clocks. CSAC: >100,000 units since 2011 (NIST; unit count vendor-via-NIST). CSAC is microwave Rb, not 10⁻¹⁸.

    NIST How Do We Know. How Do We Know What Time It Is?. https://www.nist.gov/atomic-clocks/how-do-we-know-what-time-it. As of 2025-05-28. Checked 2026-08-28. Type: Agency.NIST Clocks Galore. Clocks Galore. https://www.nist.gov/atomic-clocks/how-atomic-clocks-work/clocks-galore. As of 2026-08-21. Checked 2026-08-28. Type: Agency.
  6. E1

    Bothwell et al. Nature 2022 (NSF PAR AAM): ~100,000 ⁸⁷Sr at ~100 nK in a shallow large-waist 1D lattice. Linear frequency gradient consistent with gravitational redshift within a single millimetre-scale sample. Fractional frequency uncertainty 7.6×10⁻²¹ between two uncorrelated regions; optical atomic coherence 37 s; inferred single-region instability 3.1×10⁻¹⁸/√τ at 1 s. Predicted Earth-surface gradient −1.09×10⁻¹⁹ mm⁻¹; measured −9.8(2.3)×10⁻²⁰ mm⁻¹, consistent. Laboratory optical-lattice chronometry / metrology campus — not a field GPS replacement.

    Bothwell et al. Resolving the gravitational redshift across a millimetre-scale atomic sample. https://doi.org/10.1038/s41586-021-04349-7. As of 2022-02-16. Checked 2026-09-03. Type: Paper (Nature; NSF PAR AAM).

Magnetometers: SQUID clinical; SERF OPM research in an MSR; NV nano principle

  1. E2

    Budker & Romalis (Optical Magnetometry, arXiv physics/0611246 / Nat. Phys. 2007): SERF = spin-exchange-relaxation-free; demonstrated sensitivity >10⁻¹⁵ T/√Hz, projected fundamental limits <10⁻¹⁷ T/√Hz (citing Kominis et al. 2003). Atomic magnetometers need no cryogenics (unlike SQUIDs); measure field directly. SERF regime only for magnetic fields <~10 nT; above that, null-detector with feedback. E2 for review body (arXiv); not a clinical approval.

    Budker & Romalis. Optical Magnetometry. https://arxiv.org/pdf/physics/0611246. As of 2006-11-26 (arXiv; Nat. Phys. 2007 DOI 10.1038/nphys566). Checked 2026-09-04. Type: Paper (review; arXiv physics/0611246; Nat. Phys. 2007).
  2. E2

    Budker/Romalis: “no cryostat” ≠ “no shield/zero field”. SERF needs near-zero field; applications include bio-magnetics, NMR/MRI, space — review, no GPS-replacement claim.

    Budker & Romalis. Optical Magnetometry. https://arxiv.org/pdf/physics/0611246. As of 2006-11-26 (arXiv; Nat. Phys. 2007 DOI 10.1038/nphys566). Checked 2026-09-04. Type: Paper (review; arXiv physics/0611246; Nat. Phys. 2007).
  3. E1

    SERF OPM: femtotesla without cryogenic cooling, but in an MSR. Intrinsic noise well below 50 fT/√Hz (maker+PTB). Paper verbatim: “diagnostic and clinical relevance has not yet been demonstrated.” >100 institutes run SQUID MEG (citation, not independent).

    Elzenheimer et al. Characterizing timing parameters in commercial SERF-OPM multichannel systems for biomagnetic field sensing. https://arxiv.org/html/2509.22198v1. As of 2025-09. Checked 2026-08-28. Type: Paper.
  4. E2

    FieldLine HEDscan 128: empty-room after SSP 20±5 fT/Hz¹/². Closed-loop 350 Hz. MSR residual 150 nT → global coils to <30 nT. Higher amplitude than cryo MEG and higher background noise. Vendor coauthors.

    Alem et al. An integrated full-head OPM-MEG system based on 128 zero-field sensors. https://www.frontiersin.org/journals/neuroscience/articles/10.3389/fnins.2023.1190310/full. As of 2023-06-14. Checked 2026-08-28. Type: Paper (vendor+clinic).
  5. E1

    NV 2008: room temperature, optical polarisation. Single-NV DC with then collection ~1 µT/Hz¹/², not fT. Ensemble projection 3 fT/Hz¹/² and single proton = E3 (calculation under C=0.3).

    Taylor et al. High-sensitivity diamond magnetometer with nanoscale resolution. https://arxiv.org/html/0805.1367. As of 2008. Checked 2026-08-28. Type: Paper (proposal).

Gravimeters: absolute and hybrid; not a GPS replacement

  1. E1

    GIRAFE marine: hybrid with Honeywell Q-Flex. Ship sea state 4–6: crossing error 0.4–0.9 mGal. Fringe period ≪ vehicle acceleration → ambiguity, hence hybrid. Dead times filled classically.

    Bidel et al. 2018. Absolute marine gravimetry with matter-wave interferometry. https://www.nature.com/articles/s41467-018-03040-2. As of 2018-02-12. Checked 2026-08-28. Type: Paper.
  2. E1

    GIRAFE airborne 2017: error 1.7–3.9 mGal. ESA AirQuantumGrav 2023 + Jensen 2025: accuracy 1–2 mGal; GIRAFE no tie, no drift. Filter 40–130 s → km resolution. Platform tilt up to 20 mGal.

    Bidel et al. 2020. Absolute airborne gravimetry with a cold atom sensor. https://arxiv.org/html/1910.06666. As of 2019-10. Checked 2026-08-28. Type: Paper (J. Geodesy).ESA AirQuantumGrav. AirQuantumGrav 2023. https://earth.esa.int/eogateway/campaigns/airborne-quantum-gravimetry-airquantumgrav-2023. As of 2024-07. Checked 2026-08-28. Type: Agency/dataset.Jensen et al. Airborne gravimetry with quantum technology: observations from Iceland and Greenland. https://essd.copernicus.org/articles/17/1667/2025/. As of 2025-04-17. Checked 2026-08-28. Type: Paper.
  3. E1

    AQG 2018: sensor head ~30 kg; sensitivity 500 nm s⁻² Hz⁻¹/²; long-term <10 nm s⁻². Accuracy budget 2018 incomplete; target <50 nm s⁻² = E3. Competing interests: Muquans.

    Ménoret et al. Gravity measurements below 10⁻⁹ g with a transportable absolute quantum gravimeter. https://www.nature.com/articles/s41598-018-30608-1. As of 2018-08-17. Checked 2026-08-28. Type: Paper.

Claimed · E3

4. What is claimed, not shown

Roadmaps and projections

  1. E3

    Chronometric geodesy “3 cm”: principle, not a field campaign. Marshall: 1×10⁻¹⁹ “feasible” with a cryostat = author extrapolation.

    Aeppli / BACON. Atomic clock frequency ratios with fractional uncertainty ≤3.2×10⁻¹⁸. https://arxiv.org/html/2512.21428v1. As of 2025-12. Checked 2026-08-28. Type: Paper.
  2. E3

    CNES CARIOQA: first space-capable atom accelerometer, launch planned 2030. Status “In development.” Not flown. Not: “ESA has a quantum sensor in orbit.”

    CNES CARIOQA. CARIOQA. https://cnes.fr/en/projects/carioqa. As of 2025-01-20. Checked 2026-08-28. Type: Agency.
  3. E3

    Taylor 2008: ensemble few fT/Hz¹/²; “surpass SQUID … by more than an order of magnitude” — 2008 calculation, not a 2026 device.

    Taylor et al. High-sensitivity diamond magnetometer with nanoscale resolution. https://arxiv.org/html/0805.1367. As of 2008. Checked 2026-08-28. Type: Paper (proposal).

Constrained · Limit

5. Bottleneck and limit

What quantum sensing in 2026 is not

  1. E1

    Optical record clocks are not the SI second and not GPS. GPS payload is Rb microwave. CSAC ≠ optical.

    NIST How Do We Know. How Do We Know What Time It Is?. https://www.nist.gov/atomic-clocks/how-do-we-know-what-time-it. As of 2025-05-28. Checked 2026-08-28. Type: Agency.Marshall et al. High-stability single-ion clock with 5.5×10⁻¹⁹ systematic uncertainty. https://arxiv.org/html/2504.13071v1. As of 2025-04. Checked 2026-08-28. Type: Paper (PRL 135).NIST Clocks Galore. Clocks Galore. https://www.nist.gov/atomic-clocks/how-atomic-clocks-work/clocks-galore. As of 2026-08-21. Checked 2026-08-28. Type: Agency.
  2. E1

    Bothwell millimetre lab redshift ≠ a GPS replacement. Cs still defines the SI second (sources 9, 11); Bothwell is laboratory optical-lattice chronometry (source 18).

    NIST How Do We Know. How Do We Know What Time It Is?. https://www.nist.gov/atomic-clocks/how-do-we-know-what-time-it. As of 2025-05-28. Checked 2026-08-28. Type: Agency.NIST Fountain page. NIST’s Cesium Fountain Atomic Clocks. https://www.nist.gov/pml/time-and-frequency-division/time-realization/cesium-fountain-atomic-clocks. As of 2023-05-12. Checked 2026-08-28. Type: Agency.Bothwell et al. Resolving the gravitational redshift across a millimetre-scale atomic sample. https://doi.org/10.1038/s41586-021-04349-7. As of 2022-02-16. Checked 2026-09-03. Type: Paper (Nature; NSF PAR AAM).
  3. E1

    SERF needs near-zero field. No fT MEG without a shield. Clinic not shown. “Without a cryostat” ≠ “without a shield.”

    Elzenheimer et al. Characterizing timing parameters in commercial SERF-OPM multichannel systems for biomagnetic field sensing. https://arxiv.org/html/2509.22198v1. As of 2025-09. Checked 2026-08-28. Type: Paper.Alem et al. An integrated full-head OPM-MEG system based on 128 zero-field sensors. https://www.frontiersin.org/journals/neuroscience/articles/10.3389/fnins.2023.1190310/full. As of 2023-06-14. Checked 2026-08-28. Type: Paper (vendor+clinic).
  4. E1

    NV single-NV 2008 is microtesla, not femtotesla. fT is a volume-ensemble calculation. Nano-NMR/single proton is a projection.

    Taylor et al. High-sensitivity diamond magnetometer with nanoscale resolution. https://arxiv.org/html/0805.1367. As of 2008. Checked 2026-08-28. Type: Paper (proposal).
  5. E1

    The atom interferometer alone is fringe-ambiguous under vehicle acceleration. Airborne error 1–4 mGal, not µGal. Atom in orbit = CARIOQA plan, not flown.

    Bidel et al. 2018. Absolute marine gravimetry with matter-wave interferometry. https://www.nature.com/articles/s41467-018-03040-2. As of 2018-02-12. Checked 2026-08-28. Type: Paper.Bidel et al. 2020. Absolute airborne gravimetry with a cold atom sensor. https://arxiv.org/html/1910.06666. As of 2019-10. Checked 2026-08-28. Type: Paper (J. Geodesy).Jensen et al. Airborne gravimetry with quantum technology: observations from Iceland and Greenland. https://essd.copernicus.org/articles/17/1667/2025/. As of 2025-04-17. Checked 2026-08-28. Type: Paper.CNES CARIOQA. CARIOQA. https://cnes.fr/en/projects/carioqa. As of 2025-01-20. Checked 2026-08-28. Type: Agency.
  6. E2

    Type-III entanglement/Heisenberg is not the class of clocks/OPMs/gravimeters deployed today.

    Degen, Reinhard, Cappellaro. Quantum sensing. https://arxiv.org/html/1611.02427. As of 2017-06. Checked 2026-08-28. Type: Review (RMP 89).

6. Actors and incentives

Who keeps time, who measures fields

  1. E1

    NIST and BIPM (~450 clocks, ~90 labs) keep UTC; fountains calibrate, masers run 24/7.

    NIST How Do We Know. How Do We Know What Time It Is?. https://www.nist.gov/atomic-clocks/how-do-we-know-what-time-it. As of 2025-05-28. Checked 2026-08-28. Type: Agency.NIST F4 News. New Atomic Fountain Clock Joins Elite Group That Keeps the World on Time. https://www.nist.gov/news-events/news/2025/04/new-atomic-fountain-clock-joins-elite-group-keeps-world-time. As of 2025-04-28. Checked 2026-08-28. Type: Agency.
  2. E1

    PTB characterises commercial SERF OPMs (QuSpin, FieldLine) on timing; clinical relevance denied.

    Elzenheimer et al. Characterizing timing parameters in commercial SERF-OPM multichannel systems for biomagnetic field sensing. https://arxiv.org/html/2509.22198v1. As of 2025-09. Checked 2026-08-28. Type: Paper.
  3. E1

    The ONERA/CNES line (Bidel) and ESA AirQuantumGrav deploy atom gravimeters on ship and aircraft, hybrid.

    Bidel et al. 2018. Absolute marine gravimetry with matter-wave interferometry. https://www.nature.com/articles/s41467-018-03040-2. As of 2018-02-12. Checked 2026-08-28. Type: Paper.ESA AirQuantumGrav. AirQuantumGrav 2023. https://earth.esa.int/eogateway/campaigns/airborne-quantum-gravimetry-airquantumgrav-2023. As of 2024-07. Checked 2026-08-28. Type: Agency/dataset.

7. State of the dispute

Six things that are not “quantum sensing”

  1. E1

    Cs SI vs. optical lab clocks: more accurate ≠ defined. BACON repeatability hole against “redefinition done”.

    NIST How Do We Know. How Do We Know What Time It Is?. https://www.nist.gov/atomic-clocks/how-do-we-know-what-time-it. As of 2025-05-28. Checked 2026-08-28. Type: Agency.Marshall et al. High-stability single-ion clock with 5.5×10⁻¹⁹ systematic uncertainty. https://arxiv.org/html/2504.13071v1. As of 2025-04. Checked 2026-08-28. Type: Paper (PRL 135).Aeppli / BACON. Atomic clock frequency ratios with fractional uncertainty ≤3.2×10⁻¹⁸. https://arxiv.org/html/2512.21428v1. As of 2025-12. Checked 2026-08-28. Type: Paper.
  2. E1

    SQUID clinic vs. OPM research. Amplitude narrative vs. higher empty-room noise (Alem).

    Elzenheimer et al. Characterizing timing parameters in commercial SERF-OPM multichannel systems for biomagnetic field sensing. https://arxiv.org/html/2509.22198v1. As of 2025-09. Checked 2026-08-28. Type: Paper.Alem et al. An integrated full-head OPM-MEG system based on 128 zero-field sensors. https://www.frontiersin.org/journals/neuroscience/articles/10.3389/fnins.2023.1190310/full. As of 2023-06-14. Checked 2026-08-28. Type: Paper (vendor+clinic).
  3. E1

    CARIOQA 2030 planned vs. “ESA quantum satellite 2026”.

    CNES CARIOQA. CARIOQA. https://cnes.fr/en/projects/carioqa. As of 2025-01-20. Checked 2026-08-28. Type: Agency.

8. Open questions

  1. Budker & Romalis Nature Physics HTML (arXiv physics/0611246 opened 2026-09-04 as source 19).
  2. Barry RMP 2020 NV sensitivity review.
  3. Gerginov Metrologia 2025 body — NIST-F4 shift table.
  4. Dimarcq 2024 SI roadmap PDF.
  5. OSCAR-QUBE ISS NV — body missing.
  6. iXblue/Exail current AQG datasheet.
  7. CSAC / GPS-III Allan deviation from a maker paper.
  8. SQUID MEG noise floor 2026 (Elekta/CTF spec).
  9. Live inventory 2026: AQG devices, OPM-MEG installations, optical clocks in UTC.

9. Changes

  • v1.2-draft2026-09-04: Budker & Romalis Optical Magnetometry (source 19, arXiv physics/0611246) opened — SERF >10⁻¹⁵ T/√Hz, limit <10⁻¹⁷, regime <~10 nT, no cryogenics. E2 review; Nature Physics HTML still historically 429.
  • v1.1-draft2026-09-03: Bothwell et al. Nature 2022 (source 18, DOI 10.1038/s41586-021-04349-7, NSF PAR AAM) opened — millimetre gravitational redshift in ~100k ⁸⁷Sr, 7.6×10⁻²¹, lab not field; Cs remains the SI definition.
  • v1.0-draftFirst version from the 2026-08-28 verification log.

10. Sources

No. Source As of Checked Grade
1 Degen, C. L.; Reinhard, F.; Cappellaro, P.. Quantum sensing. https://arxiv.org/html/1611.02427. Type: Review (RMP 89). E1
2 Marshall, M. C.; Rodriguez Castillo, D. A.; Arthur-Dworschack, W. J.; Aeppli, A.; et al.. High-stability single-ion clock with 5.5×10⁻¹⁹ systematic uncertainty. https://arxiv.org/html/2504.13071v1. Type: Paper (PRL 135). E1
3 Aeppli, A.; et al. (BACON Collaboration). Atomic clock frequency ratios with fractional uncertainty ≤3.2×10⁻¹⁸. https://arxiv.org/html/2512.21428v1. Type: Paper. E1
4 Bidel, Y.; Zahzam, N.; Blanchard, C.; Bonnin, A.; Cadoret, M.; Bresson, A.; Rouxel, D.; Lequentrec-Lalancette, M. F.. Absolute marine gravimetry with matter-wave interferometry. https://www.nature.com/articles/s41467-018-03040-2. Type: Paper. E1
5 Bidel, Y.; Zahzam, N.; Bresson, A.; Blanchard, C.; Cadoret, M.; Olesen, A. V.; Forsberg, R.. Absolute airborne gravimetry with a cold atom sensor. https://arxiv.org/html/1910.06666. Type: Paper (J. Geodesy). E1
6 Ménoret, V.; Vermeulen, P.; Le Moigne, N.; Bonvalot, S.; Bouyer, P.; Landragin, A.; Desruelle, B.. Gravity measurements below 10⁻⁹ g with a transportable absolute quantum gravimeter. https://www.nature.com/articles/s41598-018-30608-1. Type: Paper. E1
7 NIST. NIST Ion Clock Sets New Record for Most Accurate Clock in the World. https://www.nist.gov/news-events/news/2025/07/nist-ion-clock-sets-new-record-most-accurate-clock-world. Type: Agency. E2
8 NIST. New Atomic Fountain Clock Joins Elite Group That Keeps the World on Time. https://www.nist.gov/news-events/news/2025/04/new-atomic-fountain-clock-joins-elite-group-keeps-world-time. Type: Agency. E2
9 NIST. How Do We Know What Time It Is?. https://www.nist.gov/atomic-clocks/how-do-we-know-what-time-it. Type: Agency. E1
10 NIST. Clocks Galore. https://www.nist.gov/atomic-clocks/how-atomic-clocks-work/clocks-galore. Type: Agency. E2
11 NIST. NIST’s Cesium Fountain Atomic Clocks. https://www.nist.gov/pml/time-and-frequency-division/time-realization/cesium-fountain-atomic-clocks. Type: Agency. E1
12 Elzenheimer, E.; Matz, H.; Zerfowski, J.; Anders, P.; Höft, M.; Rieger, R.; Soekadar, S. R.; Robinson, S.; Knappe-Grüneberg, S.. Characterizing timing parameters in commercial SERF-OPM multichannel systems for biomagnetic field sensing. https://arxiv.org/html/2509.22198v1. Type: Paper. E1
13 Alem, O.; Hughes, K. J.; et al.. An integrated full-head OPM-MEG system based on 128 zero-field sensors. https://www.frontiersin.org/journals/neuroscience/articles/10.3389/fnins.2023.1190310/full. Type: Paper (vendor+clinic). E2
14 Taylor, J. M.; Cappellaro, P.; Childress, L.; Jiang, L.; Budker, D.; Hemmer, P. R.; Yacoby, A.; Walsworth, R.; Lukin, M. D.. High-sensitivity diamond magnetometer with nanoscale resolution. https://arxiv.org/html/0805.1367. Type: Paper (proposal). E1
15 CNES. CARIOQA. https://cnes.fr/en/projects/carioqa. Type: Agency. E3
16 ESA. AirQuantumGrav 2023. https://earth.esa.int/eogateway/campaigns/airborne-quantum-gravimetry-airquantumgrav-2023. Type: Agency/dataset. E1
17 Jensen, T. E.; Dale, B.; Stokholm, A.; Forsberg, R.; Bresson, A.; Zahzam, N.; Bonnin, A.; Bidel, Y.. Airborne gravimetry with quantum technology: observations from Iceland and Greenland. https://essd.copernicus.org/articles/17/1667/2025/. Type: Paper. E1
18 Bothwell, T.; Kennedy, C. J.; Aeppli, A.; Kedar, D.; Robinson, J. M.; Oelker, E.; Staron, A.; Ye, J.. Resolving the gravitational redshift across a millimetre-scale atomic sample. https://doi.org/10.1038/s41586-021-04349-7. Type: Paper (Nature; NSF PAR AAM). E1
19 Budker, D.; Romalis, M.. Optical Magnetometry. https://arxiv.org/pdf/physics/0611246. Type: Paper (review; arXiv physics/0611246; Nat. Phys. 2007). E2

11. Uncertainty log

Overall uncertainty of this entry, bound to the verification log of 2026-08-28 plus Bothwell Nature 2022 (NSF PAR AAM) 2026-09-03 and Budker/Romalis arXiv 2026-09-04. 17 full-text openings from the log plus Bothwell AAM (E1) and Budker/Romalis arXiv (E2); Bothwell and Budker-arXiv removed from the hard unopened list. Not used as warrant: Wikipedia, vendor µGal without a paper, “quantum sensors replace GPS”, CARIOQA-2030 as hardware existence.

  • Established (layer 1): Cs SI and UTC architecture; Al⁺ lab clock; BACON ratios including the repeatability hole; Bothwell millimetre redshift (18); SERF OPM timing/clinic-not-shown; Budker/Romalis SERF review (19); GIRAFE/AQG hybrid measurements.
  • Claimed (layer 2): SI redefinition milestone; 3 cm chronometry; CARIOQA 2030; NV fT projection 2008.
  • Constrained (layer 3): optical ≠ GPS (including Bothwell lab redshift ≠ GPS replacement); OPM ≠ clinic; NV ≠ fT field device; gravimeter ≠ µGal flight without filters; Type III not deployed.

Not opened (not a warrant)

  • Budker, Romalis Nat. Phys. 2007 HTML — HTTP 429 history; arXiv body source 19.
  • Barry et al. RMP 2020 — review body not opened.
  • Allred 2002 / Kominis 2003 full texts — 10 fT abstract only.
  • Gerginov Metrologia 2025 body.
  • Dimarcq Metrologia 2024 roadmap PDF.
  • OSCAR-QUBE ISS; compact NV magnetometers 2025 (PRA 23, 034008; Dai) — snippets, not opened.
  • iXblue/Exail / Muquans AQG datasheet — timeout.
  • QuSpin/FieldLine spec PDFs; Microchip CSAC datasheet.
  • Boto NeuroImage 2017; Peters/Chu Nature 1999; Kasevich & Chu 1991.