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Multimode-polariton superradiance via Floquet engineering
by Christian Høj Johansen, Johannes Lang, Andrea Morales, Alexander Baumgärenter, Tobias Donner, Francesco Piazza
|As Contributors:||Christian H. Johansen|
|Arxiv Link:||https://arxiv.org/abs/2011.12309v2 (pdf)|
|Date submitted:||2021-09-23 09:26|
|Submitted by:||Johansen, Christian H.|
|Submitted to:||SciPost Physics|
We consider an ensemble of ultracold bosonic atoms within a near-planar cavity, driven by a far detuned laser whose phase is modulated at a frequency comparable to the transverse cavity mode spacing. We show that a strong, dispersive atom-photon coupling can be reached for many transverse cavity modes at once. The resulting Floquet polaritons involve a superposition of a set of cavity modes with a density excitation of the atomic cloud. The mutual interactions between these modes lead to distinct avoided crossings between the polaritons. Increasing the laser drive intensity, a low-lying multimode Floquet polariton softens and eventually becomes undamped, corresponding to the transition to a superradiant, self-organized phase. We demonstrate the stability of the stationary state for a broad range of parameters.
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Anonymous Report 1 on 2021-10-28 (Invited Report)
1-This manuscript is well written and organized.
2-This paper goes into great detail on how to implement multimode Floquet polaritons.
3-Overall a good resource for the community actively pursuing experiments with ultracold atomic clouds coupled to optical cavities.
1- It is unclear what is the selling point of this work. Does the platform described in this paper offer technical advantages over the Floquet polaritons demonstrated in Ref? Does it open an avenue to explore unique physical models that would otherwise be difficult with other multimode platforms?
2- The authors should provide numbers for the achievable coupling rates between the BEC cloud and the optical modes, and effective interactions between the modes, and therefore specify if this system is situated in the mean-field or many-body regime.
In their manuscript, “Multimode-polariton superradiance via Floquet engineering”, Johansen et al. describe an experimental proposal of a multimode optical platform with Floquet engineered interactions for studying many-body states of light. The authors present a system where a cloud of ultracold bosonic atoms is dispersively coupled to many transverse modes of a Fabry-Perot cavity by driving the atomic ensemble using an off-resonant laser with a periodically modulated phase. This work goes into great detail on the effects of phase modulation and careful preparation of these Floquet polaritons, thereby presenting a good resource for the AMO community pursuing BECs coupled to optical cavities.
This area of many-body cavity QED is a topic of great interest. Recent experiments have already demonstrated Floquet polaritons in a twisted cavity , a method later used for preparing a Laughlin state of photons [Clark et al. Nature 582, 41–45 (2020)], while others have already observed multimode superradiance in a degenerate confocal cavity [28-31]. It is unclear from reading this paper how this proposal offers any technical advantages over Ref or if it opens a new pathway for exploring new physical phenomena.
While I do have comments along those lines, once these are resolved the manuscript should be published in this journal.
1 - As the authors point out, this work adopts a similar idea to ref.  for creating Floquet polaritons, and features a multimode superradiant phase which has been already measured in other systems [28-31]. What is the novelty of the platform being put forward? Does it present a technical advantage over the Floquet system in ref.  or does it open a new pathway in exploring different physical models? Can this platform generate stronger mode-mode interactions or offer more flexibility in the number of modes you can couple?
2 - In Fig.5 and 6, the authors show that the modes are coupled from the observed avoided crossings. It would be informative to quantify how strong these atom-mediated multimode interactions are with respect to the polariton lifetimes. This would make the overall story clearer, validating if the system is in the mean-field or many-body regime.
3 - The authors justify the multimode superradiant phase from the renormalization of the critical atom-photon coupling and the appearance of instabilities at finite frequencies. Have the authors explored synchronization effects where the collective coupling leads to coherent emission from an ensemble of transverse modes?
4 - Have the authors considered studying this ordered phase by probing photon correlations g2 between different polariton modes?
5 - Can the authors explain what they mean by ‘deep multimode regime’ (last paragraph of section I), and how the numbers they get for the coupling strengths and interactions apply to this criteria? Are they referring to the fact that the atom-photon coupling is larger than the damping rate for multiple modes? or is the coupling larger than the free spectral range?
6 - The red crosses in Fig.4 are hardly visible due to the colormap, the authors should consider changing the cross colors