REVIEW 5 major objections 4 minor 1 cited by
Accelerated Bayesian optimization in deep cooling atoms
T0 review · 5 major / 4 minor · reviewed 2026-08-11 · deepseek-v4-flash
Pith's one-line read A modified Bayesian optimizer that also samples the largest empty hypersphere in parameter space doubles optimization efficiency on benchmark functions and, in a rubidium-87 cooling experiment, reaches about 10^8 atoms at 0.4 μK in 15…
desk verdict The experimental effort and the MHCS heuristic are real, but the paper's headline claims count iterations rather than experiments and credit the optimizer with a result that came from manual tweaks. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The engine is the Maximum Hypersphere Compensation Sampling (MHCS) step. Given a set of observed points scaled into [0,1], the algorithm forms every pair of points, treats the segment between them as a hypersphere diameter, and computes the midpoint center and radius. A hypersphere is a candidate if no other observed point lies at distance greater than R_c from its center; the algorithm picks the candidate with the largest radius and proposes its center as the next experimental setting. This proposal runs in parallel with the standard expected-improvement (EI) proposal, so each iteration adds two samples, and the EI prediction is improved because the Gaussian process surrogate sees the previously empty region. The other load-bearing machinery is the decoupled objective: PGC parameters X_P={Att,δ_c,t_i,t_m} are optimized first with the lattice off, then lattice parameters X_L={t_h,t_m,t_u,V_L} with the lattice on, using O(X)=T_a/A_s^b with b=0.5 to balance atom number and temperature.
What would settle it
Repeat the optimized sequence while measuring atom number independently (for example, by absorption imaging calibrated with the same cloud) and compare it with the time-of-flight amplitude A_s across the scanned parameter ranges; if the ratio A_s/N_a varies appreciably, the objective ranking and the reported approximately $10^{8}$ atom count are not supported.
Extended reading notes
Core claim
The central discovery claimed is that deliberately sampling the largest empty region of parameter space repairs a known weakness of acquisition-function-based Bayesian optimization, namely that expected-improvement predictions cluster in already-sampled regions and leave large parts of the space unobserved. In MHCS-BO, every observed point is scaled to [0,1], all pairwise hyperspheres (spheres whose diameters connect two observed points) are constructed, and the center of the largest hypersphere containing no observed point is selected as a second recommendation, X_MHCS, executed alongside the EI recommendation X_EI in each cycle. On five standard test functions the authors find that MHCS-BO reaches lower historical optima in roughly half the iterations of plain BO. In the atom experiment, the objective function O(X)=T_a/A_s^b (temperature divided by the b-th power of the time-of-flight signal amplitude, with b=0.5) is optimized first over the PGC parameters and then over the optical-lattice parameters; the final sequence yields approximately $10^{8}$ atoms at 0.4±0.2 μK measured by ballistic expansion. The paper frames these results as the first demonstration of this optimizer in preparing sub-μK cold atoms and as a protocol transferable to other high-dimensional experimental optimizations.
Load-bearing premise
The paper's atom-number claims rest on the assumption that the strength of the falling-atom fluorescence signal is directly proportional to the number of atoms for every parameter setting tried, and that raising that signal to the 0.5 power in the optimization score faithfully balances temperature against atom number; no independent atom-number calibration is reported.
Editorial extensions
If this is right
- On the five benchmark functions, MHCS-BO converges to better optima with 50 iterations where standard BO needs 100, so for experiments with expensive objective evaluations the method halves the number of runs needed.
- With the optimized 780 nm sequence, roughly 10^8 rubidium-87 atoms at 0.4±0.2 μK are produced within 15 minutes of optimization, a combination of large atom number and near-recoil temperature.
- Using a 1064 nm lattice and a 200 ms holding time, the same protocol produces about 2×10^8 atoms at a vertical temperature of 0.12±0.07 μK, about three times below the recoil limit.
- Simulated atom interferometry at 0.12 μK versus 4.4 μK shows fringe contrast rising from 71.2% to 99.3% and coherence time from 93 μs to 289 μs, so lower temperature directly translates into better interferometer performance.
- Optimizing the 16 parameters in two decoupled groups performs better than optimizing them all at once, avoiding the poor time-of-flight signals and misleading surrogate models seen in coupled optimization.
Reading between the lines
- Because the MHCS step is agnostic to the underlying objective, the same largest-empty-hypersphere rule could be dropped into other acquisition functions or multi-objective Bayesian optimization, potentially addressing the Pareto-front limitation the authors note.
- An independent check of the claimed atom numbers would be to calibrate the time-of-flight amplitude A_s against absorption imaging over the full optimized parameter range; if A_s is not strictly proportional to atom number, the reported 10^8 figures would shift.
- The observed temperature-floor behavior with holding time suggests the optimizer is trading atom number against temperature at the edge of the lattice well; scanning the balance coefficient b in O(X)=T_a/A_s^b would map the full trade-off curve and tell users where the reported operating point sits on it.
- The same protocol should transfer to other expensive high-dimensional alignment tasks in cold-atom and quantum-device laboratories, where standard EI commonly clusters samples and leaves sparse regions unexplored.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes Maximum Hypersphere Compensation Sampling Bayesian Optimization (MHCS-BO), a BO variant that augments expected-improvement acquisition with a point selected from the largest empty hypersphere in the observed parameter set. The authors apply the method to a 16-parameter polarization-gradient-cooling sequence enhanced by a one-dimensional optical lattice for 87Rb atoms, reporting a twofold increase in optimization efficiency and superior prediction accuracy over conventional BO, and claiming preparation of approximately 10^8 atoms at 0.4±0.2 μK within 15 minutes. The experimental work includes a 10-segment PGC timing sequence, lattice-assisted cooling, robustness scans, and comparison with manual optimization.
Significance. The experimental apparatus work is genuine and the paper contains useful detail: a 16-parameter optimization of a real cooling sequence, a long-term stability test (Appendix E), robustness scans (Fig. 7), and a ballistic-expansion temperature measurement (Fig. 8). If the claims were supported, MHCS-BO would be a valuable addition to the toolbox of automated cold-atom optimization. However, the central claims of twofold efficiency and the 0.4 μK/15-minute result are not supported by the paper's own data, and the atom-number estimates rest on an uncalibrated proxy. These issues concern the main contribution of the paper rather than presentation, so they are decisive.
major comments (5)
- [Section IV, Fig. 6(a)] The claim in the abstract and Section III that MHCS-BO provides a 'twofold increase in optimization efficiency' is contradicted by the convergence data in Fig. 6(a). The text states that BO and MHCS-BO were run for 100 and 50 iterations, respectively, 'yielding 100 sampling points,' because MHCS-BO tests two points per iteration. MHCS-BO reaches the historical global optimum at the 61st sample and BO at the 66th. Measured in experimental cycles, which is the relevant cost for a cold-atom apparatus, the improvement is about 8%, not 100%. The test-function benchmarks in Fig. 4 and Appendix C compare 50 MHCS-BO EI evaluations with 100 BO evaluations, counting MHCS evaluations as free; this is valid for computational cost but not for experimental cost, where every MHCS prediction is an additional apparatus run. The central efficiency claim therefore needs to be re-evaluated or reframed.
- [Abstract; Section IV, Fig. 8] The abstract's statement that 'approximate 10^8 cold atoms at a temperature of 0.4±0.2 μK can be achieved given the optimal parameters within 15 minutes' is not supported by the optimization results. The MHCS-BO optimized lattice parameters yield T_a=0.91 μK (Section IV, Fig. 6(d)). The 0.4 μK result is obtained only after manually increasing t_h to 20 ms and MOT loading time to 3 s (Fig. 8), which are not the parameters found by the 15-minute MHCS-BO run. The abstract should distinguish the automated optimization outcome from the subsequently hand-tuned result.
- [Section II; Appendix D] The objective function O(X)=T_a/A_s^b and the atom-number estimates throughout rely on the assumption A_s ∝ N_a, where A_s is the TOF signal amplitude. No calibration of the proportionality constant is presented, and the paper does not verify that the proportionality holds across the optimized parameter range (for example, as t_h and lattice power change the cloud size and position at the detection region, the geometric collection efficiency may vary). The 'approximately 10^8 atoms' claim is therefore unsupported. An independent atom-number measurement (e.g., fluorescence imaging calibrated by absorption imaging) is needed.
- [Appendix B; Section IV] The claim of 'superior prediction accuracy' is not demonstrated quantitatively. The Gaussian-process prediction is never evaluated against held-out experimental data; the comparisons in Fig. 4 and Fig. 6 are historical optima, not prediction error. The statement in Section IV that MHCS 'bring[s] a more precise mapping from the model to apparatus' is an interpretation, not a measurement. A prediction-error comparison on independent test points, or at least a cross-validation of the GP fit, is needed to support the claim.
- [Section III, Step 4] The definition of the MHCS candidate hypersphere contains an unclear and likely erroneous condition. Step 4 states that a hypersphere is selected as a candidate if any observed parameter satisfies |X_m − X_i| > R_c, but R_c is never defined, and the inequality direction is opposite to the usual 'empty sphere' test (one would check whether all observed points lie outside the sphere of radius R_m). Without a precise definition of R_c and the selection criterion, the algorithm is not reproducible.
minor comments (4)
- [Appendix C] The test-function benchmarks are performed only for two-dimensional functions (Fig. 12), while the experimental problem has 12-16 parameters; the claimed advantage of MHCS in high-dimensional spaces is therefore not tested by these benchmarks.
- [Section IV] The x-axis of Fig. 6(a) is not explicitly defined; because MHCS-BO runs two experiments per iteration, the reader cannot immediately tell whether 'sample' means an iteration or an experimental cycle. Please label the axis as 'experimental cycle' and define it in the caption.
- [Appendix B] In Appendix B, σ is used both for the GP standard deviation in Eq. (B3) and for the observation noise in Eq. (B1); this notational overlap is confusing and should be disambiguated.
- [Section V] The conclusion states that MHCS-BO cannot find the complete Pareto frontier, but the paper never defines a Pareto frontier for the two objectives (T_a and N_a) or explains how the scalarized objective with b=0.5 relates to it.
Circularity Check
Twofold speedup claim is constructed from chosen iteration counts, not measured; other claims are empirical.
-
other
[Section IV (Fig. 6a discussion) and Appendix C; Abstract]
"The iterations for BO and MHCS-BO are set to 100 and 50 respectively, yielding 100 sampling points. ... MHCS-BO and BO reach the historical global optimum at the 61st and 66th sample respectively. ... When comparing the performance of EI predictions between MHCS-BO and BO, datapoints obtained by MHCS are not displayed, which implies each figure FIG. 12(f)-(j) contains 50 red dots and 100 blue squares."
The factor-of-two speedup is inserted by the comparison design: BO is given 100 one-experiment iterations, MHCS-BO 50 iterations but 'yielding 100 sampling points' (two experiments per iteration). Therefore the efficiency ratio 100/50 = 2 is true by construction whenever performance is measured per iteration, and in the test-function benchmark this is reinforced by hiding the MHCS evaluations ('datapoints obtained by MHCS are not displayed'). Measured in actual experimental samples, the same paragraph reports 61 versus 66 samples, an ~8% gain, not a twofold one. The headline 'twofold increase in optimization efficiency' is thus a renamed iteration-count ratio rather than an independent experimental speedup.
full rationale
The main circularity is in the quantitative headline claim. The abstract states 'MHCS-BO demonstrates a twofold increase in optimization efficiency,' but the paper's own experimental comparison fixes BO at 100 iterations and MHCS-BO at 50 iterations while each MHCS-BO iteration conducts two experiments, so the 2x factor is an artifact of iteration-count bookkeeping. Using the physically relevant sample count, the paper reports 61 versus 66 samples, an ~8% improvement. The test-function comparison in Appendix C compounds this by omitting the MHCS evaluations, yielding '50 red dots and 100 blue squares' even though MHCS-BO actually performed 50 additional evaluations. This is not a fitted parameter renamed as a prediction, but it is a central quantitative claim that reduces by construction to the chosen comparison convention. The rest of the paper is not circular: the measured atom temperatures, the ballistic-expansion fit, and the TOF optimization results are genuine experimental outputs; the MHCS algorithm's empty-hypersphere exploration rule is defined independently of the objective function; and the citation to the authors' previous work [34] only describes the apparatus and does not carry a load-bearing mathematical claim. The uncalibrated A_s ∝ N_a assumption is a measurement-validity weakness rather than a circular derivation, since the final temperatures and atom-number estimates are not derived from the surrogate model. Overall, the experimental atom-temperature result is independent, but the primary efficiency claim suffers from partial circularity.
Assumptions & free parameters
free parameters (3)
- b (balancing coefficient) =
0.5
- GP kernel length scale (initial) =
0.01 (range 0.001 to 5)
- Initial dataset size =
10 random samples
assumptions (4)
- domain assumption The objective function is a sample from a Gaussian process with an RBF kernel and Gaussian observation noise.
- domain assumption TOF signal amplitude A_s is proportional to atom number N_a.
- ad hoc to paper The MHCS candidate hypersphere, defined by a pair of observed points, identifies a useful unexplored region.
- domain assumption PGC and lattice parameters can be optimized sequentially (decoupled) without losing the global optimum.
Cite this review
Pith. "Pith review of Accelerated Bayesian optimization in deep cooling atoms." pith.science (2026). https://pith.science/paper/NZPVPX3X
@misc{pith2026241211793,
author = {Pith},
title = {Pith review of: Accelerated Bayesian optimization in deep cooling atoms},
year = {2026},
howpublished = {\url{https://pith.science/paper/NZPVPX3X}},
note = {Machine review of arXiv:2412.11793}
}
abstract
Laser cooling, which cools atomic and molecular gases to near absolute zero, is the crucial initial step for nearly all atomic gas experiments. However, fast achievement of numerous sub-$\mu$K cold atoms is challenging. To resolve the issue, we propose and experimentally validate an intelligent polarization gradient cooling approach enhanced by optical lattice, utilizing Maximum Hypersphere Compensation Sampling Bayesian Optimization (MHCS-BO). MHCS-BO demonstrates a twofold increase in optimization efficiency and superior prediction accuracy compared to conventional Bayesian optimization. Finally, approximate $10^8$ cold atoms at a temperature of 0.4$\pm$0.2 $\mu$K can be achieved given the optimal parameters within 15 minutes. Our work provides an intelligent protocol, which can be generalized to other high-dimension parameter optimization problems, and paves way for preparation of ultracold atom in quantum experiments.
Figures
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Forward citations
Cited by 1 Pith paper
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LLM-based Multi-Agent Copilot for Quantum Sensor
An LLM multi-agent framework autonomously optimized a rubidium cold-atom cooling apparatus to sub-microkelvin temperatures and flagged injected equipment faults via correlation analysis.
Reference graph
Works this paper leans on
- [1]
-
[2]
K. M. Jones, E. Tiesinga, P. D. Lett, and P. S. Julienne, Ultra- cold photoassociation spectroscopy: Long-range molecules and atomic scattering, Rev. Mod. Phys.78, 483 (2006)
work page 2006
-
[3]
M. S. Safronova, D. Budker, D. DeMille, D. F. J. Kimball, A. Derevianko, and C. W. Clark, Search for new physics with atoms and molecules, Rev. Mod. Phys.90, 025008 (2018)
2018
- [4]
-
[5]
A. N. Ciavarella, S. Caspar, H. Singh, and M. J. Savage, Prepa- ration for quantum simulation of the (1 + 1)-dimensional o(3) nonlinearσmodel using cold atoms, Phys. Rev. A107, 042404 (2023)
work page 2023
-
[6]
R. Ott, T. V . Zache, F. Jendrzejewski, and J. Berges, Scalable Cold-Atom Quantum Simulator for Two-Dimensional QED, Phys. Rev. Lett.127, 130504 (2021)
work page 2021
-
[7]
J. C. Halimeh, I. P. McCulloch, B. Yang, and P. Hauke, Tun- ing the topologicalθ-angle in cold-atom quantum simulators of gauge theories, PRX Quantum3, 040316 (2022)
work page 2022
-
[8]
A. Cao, W. J. Eckner, T. Lukin Yelin, A. W. Young, S. Jandura, L. Yan, K. Kim, G. Pupillo, J. Ye, N. Darkwah Oppong, and A. M. Kaufman, Multi-qubit gates and Schrödinger cat states in an optical clock, Nature634, 315 (2024)
2024
Show all 39 references
-
[9]
J.-M. Mol, L. Esguerra, M. Meister, D. E. Bruschi, A. W. Schell, J. Wolters, and L. Wörner, Quantum memories for fun- damental science in space, Quantum Sci. Technol.8, 024006 (2023)
2023
-
[10]
I. V . V ovcenko, V . Yu. Shishkov, and E. S. Andrianov, Dephasing-assisted entanglement in a system of strongly cou- pled qubits, Opt. Express29, 9685 (2021)
2021
-
[11]
Kasevich and S
M. Kasevich and S. Chu, Atomic interferometry using stimu- lated Raman transitions, Phys. Rev. Lett.67, 181 (1991)
1991
-
[12]
Ejtemaee and P
S. Ejtemaee and P. C. Haljan, 3D Sisyphus Cooling of Trapped Ions, Phys. Rev. Lett.119, 043001 (2017)
2017
-
[13]
Y . Wang, Y . Li, J. Wu, W. Liu, J. Hu, J. Ma, L. Xiao, and S. Jia, Hybrid evaporative cooling of 133Cs atoms to Bose-Einstein condensation, Opt. Express29, 13960 (2021)
2021
-
[14]
Zohar, Y
E. Zohar, Y . Florshaim, O. Zilberman, A. Stern, and Y . Sagi, Degenerate Raman sideband cooling of 40K atoms, Phys. Rev. A106, 063111 (2022)
2022
-
[15]
J. E. Debs, P. A. Altin, T. H. Barter, D. Döring, G. R. Dennis, G. McDonald, R. P. Anderson, J. D. Close, and N. P. Robins, Cold-atom gravimetry with a Bose-Einstein condensate, Phys. Rev. A84, 033610 (2011)
2011
-
[16]
Louchet-Chauvet, T
A. Louchet-Chauvet, T. Farah, Q. Bodart, A. Clairon, A. Lan- dragin, S. Merlet, and F. Pereira Dos Santos, The influence of transverse motion within an atomic gravimeter, New J. Phys. 13, 065025 (2011)
2011
-
[17]
M. H. Anderson, J. R. Ensher, M. R. Matthews, C. E. Wieman, and E. A. Cornell, Observation of Bose-Einstein Condensation in a Dilute Atomic Vapor, Science269, 198 (1995)
1995
-
[18]
K. M. R. van der Stam, E. D. van Ooijen, R. Meppelink, J. M. V ogels, and P. van der Straten, Large atom number Bose-Einstein condensate of sodium, Rev. Sci. Instrum.78, 10.1063/1.2424439 (2007)
2007 doi
-
[19]
W. Xu, T. Šumarac, E. H. Qiu, M. L. Peters, S. H. Cantú, Z. Li, A. Menssen, M. D. Lukin, S. Colombo, and V . Vuleti ´c, Bose- Einstein Condensation by Polarization Gradient Laser Cooling, Phys. Rev. Lett.132, 233401 (2024)
2024
-
[20]
Wei and C
C. Wei and C. C. N. Kuhn, Laser cooling of rubidium atoms in a 2D optical lattice, J. Mod. Opt.65, 1226 (2018)
2018
-
[21]
P. B. Wigley, P. J. Everitt, A. van den Hengel, J. W. Bastian, M. A. Sooriyabandara, G. D. McDonald, K. S. Hardman, C. D. Quinlivan, P. Manju, C. C. N. Kuhn, I. R. Petersen, A. N. Luiten, J. J. Hope, N. P. Robins, and M. R. Hush, Fast machine- learning online optimization of u...
2016
-
[22]
Carleo and M
G. Carleo and M. Troyer, Solving the quantum many-body problem with artificial neural networks, Science355, 602 (2017)
2017
-
[23]
Torlai, G
G. Torlai, G. Mazzola, J. Carrasquilla, M. Troyer, R. Melko, and G. Carleo, Neural-network quantum state tomography, Nat. Phys.14, 447 (2018)
2018
-
[24]
Rohringer, R
W. Rohringer, R. Bücker, S. Manz, T. Betz, Ch. Koller, M. Gö- bel, A. Perrin, J. Schmiedmayer, and T. Schumm, Stochastic optimization of a cold atom experiment using a genetic algo- rithm, Appl. Phys. Lett.93, 264101 (2008)
2008
-
[25]
Palittapongarnpim, P
P. Palittapongarnpim, P. Wittek, E. Zahedinejad, S. Vedaie, and B. C. Sanders, Learning in quantum control: High-dimensional global optimization for noisy quantum dynamics, Neurocom- puting268, 116 (2017)
2017
-
[26]
H. Che, A. Li, J. Fang, X. Chen, and F.-J. Qin, Interference fringe fitting of atom gravimeter based on fitness particle swarm optimization, AIP Advances12, 075211 (2022)
2022
-
[27]
Q. Liu, Y . Xie, L. Li, A. Liang, W. Li, H. Chen, S. Fang, Q. Qu, L. Liu, B. Wang, and D. Lü, Multiparameter autonomous op- timization system for ultracold atomic experiments based on artificial neural network, Chin. J. Lasers48, 2412001 (2021)
2021
-
[28]
A. D. Tranter, H. J. Slatyer, M. R. Hush, A. C. Leung, J. L. Everett, K. V . Paul, P. Vernaz-Gris, P. K. Lam, B. C. Buchler, and G. T. Campbell, Multiparameter optimisation of a magneto- optical trap using deep learning, Nat. Commun.9, 4360 (2018)
2018
-
[29]
Vendeiro, J
Z. Vendeiro, J. Ramette, A. Rudelis, M. Chong, J. Sin- clair, L. Stewart, A. Urvoy, and V . Vuleti´c, Machine-learning- accelerated Bose-Einstein condensation, Phys. Rev. Res.4, 043216 (2022)
2022
-
[30]
LeDesma, K
C. LeDesma, K. Mehling, J. Shao, J. D. Wilson, P. Axelrad, M. Nicotra, D. Z. Anderson, and M. Holland, Demonstration of a programmable optical lattice atom interferometer, Phys. Rev. Res.6, 043120 (2024)
2024
-
[31]
Reinschmidt, J
M. Reinschmidt, J. Fortágh, A. Günther, and V . V . V olchkov, Reinforcement learning in cold atom experiments, Nat. Com- mun.15, 8532 (2024)
2024
-
[32]
A. J. Barker, H. Style, K. Luksch, S. Sunami, D. Garrick, F. Hill, C. J. Foot, and E. Bentine, Applying machine learn- ing optimization methods to the production of a quantum gas, Mach. Learn.: Sci. Technol.1, 015007 (2020)
2020
-
[33]
S. Xu, P. Kaebert, M. Stepanova, T. Poll, M. Siercke, and S. Ospelkaus, Maximizing the capture velocity of molecular magneto-optical traps with Bayesian optimization, New J. Phys. 23, 063062 (2021)
2021
-
[34]
Liang, S
C. Liang, S. Gao, J. Liu, G. Wang, S. Yan, J. Yang, L. Zhu, and X. Ma, Multi-parameter optimization of polarization gradient cooling for 87Rb atoms based on reinforcement learning, Opt. Express32, 40364 (2024)
2024
-
[35]
Anton, V
O. Anton, V . A. Henderson, E. Da Ros, I. Sekulic, S. Burger, P.- I. Schneider, and M. Krutzik, Review and experimental bench- marking of machine learning algorithms for efficient optimiza- tion of cold atom experiments, Mach. Learn.: Sci. Technol.5, 025022 (2024)
2024
-
[36]
X. Yao, Y . Liu, and G. Lin, Evolutionary programming made faster, IEEE Trans. Evolut. Comput.3, 82 (1999)
1999
-
[37]
Xin and S
W. Xin and S. Yuan, Research progress of cold atomic tempera- ture measurement methods, Chin. J. Sci. Instrum.44, 70 (2024)
2024
-
[38]
T. G. Petelski,Atom interferometers for precision gravity mea- surements, Phd dissertation, Pierre and Marie Curie University, Paris (2005). FIG. 10. Schematic diagram of the laser system. ECDL: External Cavity Diode Laser, FL: Fiber Laser, PBS: Polarizing Beam Split- ter, BC:...
2005
-
[39]
The adaptive kernel function can automatically adjust its shape based on the data characteristics, thus flexibly adapting to changes in different data distributions and features. Based on this model, the average valueµand standard deviationδat Xs, a point sampled in parameter ...
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