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A ship-in-a-bottle quantum gas microscope for magnetic mixtures
by Maximilian Sohmen, Manfred J. Mark, Markus Greiner, Francesca Ferlaino
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Quantum gas microscopes are versatile and powerful tools for fundamental science as well as promising candidates for enticing applications such as in quantum simulation or quantum computation. Here we present a quantum gas microscopy setup for experiments with highly magnetic atoms of the lanthanoid elements erbium and dysprosium. Our setup features a non-magnetic, non-conducting, large-working-distance, high-numerical-aperture, in-vacuum microscope objective, mounted inside a glue-free quartz glass cell. The quartz glass cell is enclosed by a compact multi-shell ferromagnetic shield that passively suppresses external magnetic field noise by a factor of more than a thousand. Our setup will enable direct manipulation and probing of the rich quantum many-body physics of dipolar atoms in optical lattices, and bears the potential to put exciting theory proposals - including exotic magnetic phases and quantum phase transitions - to an experimental test.
Submission & Refereeing History
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- Report 3 submitted on 2023-08-08 17:13 by Anonymous
- Report 2 submitted on 2023-07-20 13:40 by Anonymous
- Report 1 submitted on 2023-07-17 14:06 by Anonymous
Reports on this Submission
- Cite as: Anonymous, Report on arXiv:scipost_202306_00014v1, delivered 2023-08-08, doi: 10.21468/SciPost.Report.7625
The manuscript by Sohmen et al. reports on a design study of elements required to realize a quantum gas microscope for dipolar atomic mixtures including assembly descriptions into a quantum gas apparatus. Microscopy of magnetic erbium atoms in an optical lattice has been demonstrated only recently, with spectacular demonstrations of strongly correlated phases emerging from long-range dipolar interactions (see arXiv:2306.00888). The manuscript thus accompanies these exciting advances in the field of cold atom research and provides interesting technical details associated with the construction of a quantum gas microscope for dipolar lattice experiments. Following a detailed introduction to past achievements and typical realizations of quantum gas microscopy and future research directions for dipolar mixtures, the core of the manuscript elaborates on the design of the in-vacuum objective and the magnetic shielding. Before I can recommend publication, the authors should address the following list of questions and comments:
- The recent achievement of quantum gas microscopy for dipolar atoms should be emphasized more prominently in the manuscript. A suitable paragraph for this would be §3 of the introduction. Also later in the manuscript, it is stated: “Many more already exist or might become apparent once a dipolar quantum gas microscope is in operation.” This should be corrected accordingly.
- Table I: The authors should provide more precise (literature) values for the linewidths of the listed transitions in Er and Dy.
- Introduction, section B: The large masses of Er and Dy are highlighted as key features providing small recoil energies. I agree that this may help e.g. for high-fidelity imaging. On the other hand, doesn’t the small recoil energy in a lattice system also necessitates lower temperature scales?
- Microscope objective design: For a technical paper, there is little information provided on the optical design of the objective. A figure indicating the lens assembly of the five singlets with focal lengths, geometries, and used materials would be very helpful. Additionally, the authors mention chromatic correction also at 626nm, but Fig. 2 and also Table III only specify simulated performance at 401 and 421nm. The plots and the table should be completed by the third wavelength. I suppose the plots in Fig. 2 and the values for Table III are extract from a Zeemax model provided by the manufacturer. This should be indicated. Finally, when Fig. 2 is referenced on p. 6, I am missing a discussion of the most central results of the objective analysis. For example, what do the authors extract in view of the performance of the microscope from panels (c) and (d) showing OPD and Modulus of OFT.
- On page 5, the authors describe a crucial element of the lattice architecture, namely the small mirror glued on the last lens element of the objective. Is this last lens surface flat? How is the alignment of this mirror done?
- On page 7, the authors mention an achromatic telefocus system with reduced physical lengths for imaging. It would be helpful to provide a sketch of that system or at least a more detailed description in the text.
- On page 7, the authors describe the quartz cell: which synthetic quarz glass is used? This would be valuable information specifically for UV applications.
- On page 9, the authors describe the bakeout and mention that no lifetime changes have been measured for the quantum gas after opening the gate valve to the microscope chamber. I suppose this is a statement for a gas in the main chamber? This should be indicated. Also, the value for the measured lifetime should be given. Does it confirm the 10^-11mbar, possibly measured on a gauge?
- Chapter III. The authors should provide a benchmark number for magnetic field stability they aim to achieve in their setup together with a more in-depth discussion of the associated physics they aim to observe.
- The manuscript does not mention water cooling for the microscope coils. What are the maximum field values that can be applied to this setup for typical duties cycles without major coil heating?
- The authors mention in the text that they have verified S~10^3 shielding factor at DC. What are simulated/measured AC shielding factors, and did the authors do a systematic measurement of the AC response of the shield?
- Paper title: The title of the paper suggests the realization of an operating quantum gas microscope tested with atoms. I would suggest to change the title in a way that clarifies that this manuscript is a design study and characterization of experimental components needed to perform quantum gas microscopy for magnetic mixtures.
- Cite as: Anonymous, Report on arXiv:scipost_202306_00014v1, delivered 2023-07-20, doi: 10.21468/SciPost.Report.7541
In their manuscript, Sohmen et al. present a well-written and detailed description of building and characterizing a quantum gas microscopy setup for probing erbium-dysprosium mixtures that is mounted inside the vacuum cell and shielded from magnetic fields.
The introduction detailly summarizes the scientific developments of quantum gas microscopy during the past 15 years and motivates clearly that the mixture of erbium and dysprosium offers novel and exciting research with such a device.
The authors detail the building and design process of the most important parts of the additional apparatus, i.e., the microscope objective, its vacuum integration, and the magnetic shielding, in three separate parts. Thereby, they consider different options and solutions with respective advantages and disadvantages in a very clear and understandable way and explain their design choices in detail. Moreover, they characterize crucial parts of the setup such as the optical performance and the magnetic shielding.
In the last part of the manuscript, the features of the constructed quantum gas microscope are summarized and future steps are outlined.
Due to the high number of technical details and the clear and detailed description of design possibilities and choices, the manuscript is a relevant contribution to the field of quantum gas microscopy and will be highly appreciated by experimentalists.
However, I have a few questions and minor comments before I can recommend publication.
List of Comments:
- The referencing of figures and tables should be done in a consistent and ordered way. During reading, I found figures mentioned directly in the text as ‘Figure’ and ‘Fig.’, in ‘()’, in ‘’, with ‘cf. …’, with ‘see …’. Furthermore, figure 3(a) is mentioned before figure 2 and figure 7 before figure 6 in the main text. Moreover, I did not find a reference to figure 10 at all – I guess that the second time Fig. 9 is referenced Fig. 10 is meant to be referenced. All these issues are distracting while reading an otherwise very well-written and interesting manuscript.
- ‘Owing to the superior signal-to-noise ratio,site-resolved detection is usually based on fluorescence imaging.’ What are other imaging techniques that fluorescence imaging is superior to?
Being not an expert on erbium and dysprosium I have several questions concerning the features of the individual species as well as the mixture:
- ’Most importantly, of course, erbium and dysprosium feature large permanent magnetic dipole moments of 7 μB and 10 μB, respectively, where μB is the Bohr magneton (cf. rubidium: 1 μB).’ Can the authors further comment on the consequences for DDI due to this one order of magnitude increased magnetic dipole moment compared to Rb?
- ‘The erbium and dysprosium isotopes offer dense Feshbach spectra with a comfortable number of broad resonances at easily accessible field strengths, favourable for contact interaction tuning [51–53] or molecule formation .’ Having several control knobs at hand is in general good, but can such ‘dense’ Feshbach spectra lead to additional obstacles in contrast to other species? If yes, how can these be approached?
- ‘Note that the broadest transitions of erbium and dysprosium are in the blue part of the visible spectrum, hence yield a high resolution according to the Abbe limit.’ I totally agree with this sentence, but I think it should be also mentioned that already in this regime a lot of standard optical elements widely used do not perform in this limit. E.g., lenses show a steep dispersion of the refractive index at these wavelengths.
- ‘$λ_l$ is tuned to a value where the polarizability vanishes for species A, $\alpha_A(λ_l$) ≈ 0, but not for species B.’ Citations for other mixtures fit here. Can the wavelength be specified/calculated or is there already a publication for the targeted mixture?
I. Microscope Objective, B:
- ‘The objective’s optical design values are summarized in Table III; moreover, some important calculated characteristics are plotted in Fig. 2.’ How were these values and characteristics obtained? If provided by the manufacturer it should be mentioned, if obtained by optics simulation the program used should be mentioned.
I. Microscope Objective, C:
- ‘Therefore we used numerical methods to design a telefocus system which consists solely of stock lenses, has a large effective focal length (6.2 m) but a small physical length (1.1 m) and is fully achromatic at 401 and 421 nm.’ This system’s design parameters and a few details could be included in an appendix. Has this system's "fully achromatic" behavior also been tested experimentally to rigorously rule out that the observed focal shift stems from the objective?
III. Magnetic environment, A:
- ‘Even though FEM simulations (Section IIIC) indicate …’ Which program has been used in these simulations? From the figures shown, I would guess COMSOL, but which version and which module?
III. Magnetic environment, B:
- ‘Estimated requirements for our future microscope experiments suggested to target a shielding factor S ∼ 10^3.’ How is this estimate carried out? What are the expected consequences and advantages for the experiment operated later?
- Cite as: Anonymous, Report on arXiv:scipost_202306_00014v1, delivered 2023-07-17, doi: 10.21468/SciPost.Report.7520
In 'A ship-in-a-bottle quantum gas microscope for magnetic mixtures' M. Sohmen and coauthors present a clean, well written and detailed description of the state of the art, the decision process, the building and the characterisation of a quantum gas microscope that is mounted inside the vacuum cell and externally shielded from magnetic fields by a passive mu-metal system.
The paper introduction is well written, and the authors describe in detail the scientific reasons and the solutions that have been developed in the last 15 years to allow the detection of single atoms by using an optical microscope in ultracold gas experiments.
The different solutions, their advantages and disadvantages are listed and catalogued in a very intuitive and useful way. The different approaches are then discussed with particular attention to their applicability in erbium and dysprosium experiments.
The last part of the paper is dedicated to discussing the solutions that have been found for magnetic field control and shielding. Many technical details are really appreciated by experimentalist readers.
List of comments:
- Introduction: B, paragraph 'DDI-mediated lattice'.
The authors present the interesting situation of a species dependent lattice. This is not a novelty in the field, and it has been discussed for spin mixtures as well.
Citations are necessary. Examples of experiments are
Scattering in Mixed Dimensions with Ultracold Gases. G. Lamporesi et al, Phys. Rev. Lett. 104, 153202
Slow Thermalization between a Lattice and Free Bose Gas, David C. McKayet al Phys. Rev. Lett. 111, 063002
Theory citations are numerous and can also be found in the previous two papers.
The idea requires finding a wavelength suitable for the species-dependent lattice. Is there any idea or prediction for erbium and dysprosium? The spectra should be well known to give a rough idea of the location.
- Microscope objective: Table II
The table contains a very clear catalogue of advantages and disadvantages of the possible microscope solution. The citation list is, however, confusing and not clear to me. Are the citations chosen as exemplary or is there a completeness intention behind them? In this last case, many citations are missing, or a justification of the chosen citations must be provided. Missing citations, for example,
Rev Sci Inst 91 063202 (2020)
Rev Sci Inst 90 053201 (2019)
Optics Express 28(24) 36122 (2020)
- The 'Three ruby balls' sentence appears twice in different places with complementary information. Supposed to be so?
- III Magnetic environment: B.
The motivations for the shielding and the requirements are well written.
However, the citations 99–101 are relatively poor and incomplete compared to the completeness that characterises the part dedicated to the microscope.
I would suggest a more detailed state of the art.
Especially to what it concerns the comparison with the shield system that is presented in 100. The four-layer system, the choice of material, and the geometry are practically identical to the one here presented, and more credits must be given.
- III Magnetic environment: C.
The authors report the experimentally measured magnetic shield factors in a very fast and not very detailed way. For example, a measurement as ref 100 would be much more satisfactory, if one compared how many experimental graphs are presented for the microscope.