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Collective strong coupling of thermal atoms to integrated microring resonators

Xiaoyu Cheng1,*, Benyamin Shnirman1,2, Alexandra Köpf1,2, Guangcanlan Yang3, Hong X. Tang3, Hadiseh Alaeian4,5, Tilman Pfau1, and Robert Löw1

  • *Contact author: xycheng1123@gmail.com
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Phys. Rev. Research 8, 043063 – Published 16 October, 2026

DOI: https://doi.org/10.1103/bkxk-dt49

Abstract

Strong coupling between atomic ensembles and high-quality optical cavities enables collective and nonlinear phenomena that are central to cavity quantum electrodynamics (cQED). Many experiments have been performed on this topic, with most of them focusing on cold atoms. Here, we experimentally demonstrate collective strong coupling between thermal rubidium vapor and high-quality silicon nitride microring resonators (MRRs) on an integrated photonic chip. We observe cavity-mode splitting, with a measured collective coupling strength of gN/2π≈1GHz and a collective cooperativity of CN≈2 at 110∘C, indicating coherent energy exchange between the atomic ensemble and the cavity mode despite rapid decoherence in the thermal vapor system. We infer an average of 20 atoms effectively participating in the collective interaction, yielding a single-atom cooperativity of C0=0.1 and approaching the single-atom strong-coupling regime. Our results establish the integrated thermal vapor MRR platform as a robust, compact, and scalable system for studying collective and nonlinear phenomena in cQED.

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References (52)

  1. E. M. Purcell, H. C. Torrey, and R. V. Pound, Spontaneous emission probabilities at radio frequencies, Phys. Rev. 69, 37 (1946).
  2. E. Jaynes and F. Cummings, Comparison of quantum and semiclassical radiation theories with application to the beam maser, Proc. IEEE 51, 89 (1963).
  3. M. Tavis and F. W. Cummings, Exact solution for an N-molecule-radiation-field Hamiltonian, Phys. Rev. 170, 379 (1968).
  4. M. G. Raizen, R. J. Thompson, R. J. Brecha, H. J. Kimble, and H. J. Carmichael, Normal-mode splitting and linewidth averaging for two-state atoms in an optical cavity, Phys. Rev. Lett. 63, 240 (1989).
  5. Y. Zhu, D. J. Gauthier, S. E. Morin, Q. Wu, H. J. Carmichael, and T. W. Mossberg, Vacuum Rabi splitting as a feature of linear-dispersion theory: Analysis and experimental observations, Phys. Rev. Lett. 64, 2499 (1990).
  6. R. J. Thompson, G. Rempe, and H. J. Kimble, Observation of normal-mode splitting for an atom in an optical cavity, Phys. Rev. Lett. 68, 1132 (1992).
  7. S. Haroche and J. Raimond, Radiative properties of Rydberg states in resonant cavities, Adv. At. Mol. Phys. 20, 347 (1985).
  8. A. Boca, R. Miller, K. M. Birnbaum, A. D. Boozer, J. McKeever, and H. J. Kimble, Observation of the vacuum Rabi spectrum for one trapped atom, Phys. Rev. Lett. 93, 233603 (2004).
  9. P. Maunz, T. Puppe, I. Schuster, N. Syassen, P. W. H. Pinkse, and G. Rempe, Normal-mode spectroscopy of a single-bound-atom–cavity system, Phys. Rev. Lett. 94, 033002 (2005).
  10. H. Takahashi, E. Kassa, C. Christoforou, and M. Keller, Strong coupling of a single ion to an optical cavity, Phys. Rev. Lett. 124, 013602 (2020).
  11. C. J. Hood, T. W. Lynn, A. C. Doherty, A. S. Parkins, and H. J. Kimble, The atom-cavity microscope: Single atoms bound in orbit by single photons, Science 287, 1447 (2000).
  12. J. McKeever, A. Boca, A. D. Boozer, R. Miller, J. R. Buck, A. Kuzmich, and H. J. Kimble, Deterministic generation of single photons from one atom trapped in a cavity, Science 303, 1992 (2004).
  13. Y. Liu, Z. Wang, P. Yang, Q. Wang, Q. Fan, S. Guan, G. Li, P. Zhang, and T. Zhang, Realization of strong coupling between deterministic single-atom arrays and a high-finesse miniature optical cavity, Phys. Rev. Lett. 130, 173601 (2023).
  14. Y. Colombe, T. Steinmetz, G. Dubois, F. Linke, D. Hunger, and J. Reichel, Strong atom–field coupling for Bose–Einstein condensates in an optical cavity on a chip, Nature (London) 450, 272 (2007).
  15. P. Samutpraphoot, T. Đorđević, P. L. Ocola, H. Bernien, C. Senko, V. Vuletić, and M. D. Lukin, Strong coupling of two individually controlled atoms via a nanophotonic cavity, Phys. Rev. Lett. 124, 063602 (2020).
  16. E. Will, L. Masters, A. Rauschenbeutel, M. Scheucher, and J. Volz, Coupling a single trapped atom to a whispering-gallery-mode microresonator, Phys. Rev. Lett. 126, 233602 (2021).
  17. C. Junge, D. O’Shea, J. Volz, and A. Rauschenbeutel, Strong coupling between single atoms and nontransversal photons, Phys. Rev. Lett. 110, 213604 (2013).
  18. T. Aoki, B. Dayan, E. Wilcut, W. P. Bowen, A. S. Parkins, T. J. Kippenberg, K. J. Vahala, and H. J. Kimble, Observation of strong coupling between one atom and a monolithic microresonator, Nature (London) 443, 671 (2006).
  19. T.-H. Chang, X. Zhou, M. Zhu, B. M. Fields, and C.-L. Hung, Efficiently coupled microring circuit for on-chip cavity QED with trapped atoms, Appl. Phys. Lett. 117, 174001 (2020).
  20. H. Alaeian, R. Ritter, M. Basic, R. Löw, and T. Pfau, Cavity QED based on room temperature atoms interacting with a photonic crystal cavity: A feasibility study, Appl. Phys. B 126, 25 (2020).
  21. L. Stern and U. Levy, Transmission and time delay properties of an integrated system consisting of atomic vapor cladding on top of a micro ring resonator, Opt. Express 20, 28082 (2012).
  22. R. Ritter, N. Gruhler, W. H. P. Pernice, H. Kübler, T. Pfau, and R. Löw, Coupling thermal atomic vapor to an integrated ring resonator, New J. Phys. 18, 103031 (2016).
  23. D. W. Vernooy, A. Furusawa, N. P. Georgiades, V. S. Ilchenko, and H. J. Kimble, Cavity QED with high-Q whispering gallery modes, Phys. Rev. A 57, R2293 (1998).
  24. R. Zektzer, X. Lu, K. T. Hoang, R. Shrestha, S. Austin, F. Zhou, A. Chanana, G. Holland, D. Westly, P. Lett, A. V. Gorshkov, and K. Srinivasan, Strong interactions between integrated microresonators and alkali atomic vapors: Towards single-atom, single-photon operation, Optica 11, 1376 (2024).
  25. S. T. Chu, B. E. Little, W. Pan, T. Kaneko, S. Sato, and Y. Kokubun, Eight-channel add-drop filter using vertically coupled microring resonators over a cross grid, IEEE Photonics Technol. Lett. 11, 691 (1999).
  26. B. E. Little, S. T. Chu, W. Pan, and Y. Kokubun, Microring resonator arrays for VLSI photonics, IEEE Photonics Technol. Lett. 12, 323 (2000).
  27. A. Saxena, A. Manna, R. Trivedi, and A. Majumdar, Realizing tight-binding Hamiltonians using site-controlled coupled cavity arrays, Nat. Commun. 14, 5260 (2023).
  28. R. Ritter, N. Gruhler, H. Dobbertin, H. Kübler, S. Scheel, W. Pernice, T. Pfau, and R. Löw, Coupling thermal atomic vapor to slot waveguides, Phys. Rev. X 8, 021032 (2018).
  29. A. Skljarow, H. Kübler, C. S. Adams, T. Pfau, R. Löw, and H. Alaeian, Purcell-enhanced dipolar interactions in nanostructures, Phys. Rev. Res. 4, 023073 (2022).
  30. X. Liu, A. W. Bruch, Z. Gong, J. Lu, J. B. Surya, L. Zhang, J. Wang, J. Yan, and H. X. Tang, Ultra-high-Q UV microring resonators based on a single-crystalline AlN platform, Optica 5, 1279 (2018).
  31. H. J. Kimble, Strong interactions of single atoms and photons in cavity QED, Phys. Scr. T76, 127 (1998).
  32. C. Xiong, X. Sun, K. Y. Fong, and H. X. Tang, Integrated high frequency aluminum nitride optomechanical resonators, Appl. Phys. Lett. 100, 171111 (2012).
  33. H.-J. Chen, K. Colburn, P. Liu, H. Yan, H. Hou, J. Ge, J.-Y. Liu, P. Lehan, Q.-X. Ji, Z. Yuan, D. Bouwmeester, C. Holmes, J. Gates, H. Blauvelt, and K. Vahala, Towards fibre-like loss for photonic integration from violet to near-infrared, Nature (London) 649, 338 (2026).
  34. D. Leykam, S. Mittal, M. Hafezi, and Y. D. Chong, Reconfigurable topological phases in next-nearest-neighbor coupled resonator lattices, Phys. Rev. Lett. 121, 023901 (2018).
  35. A. Reiserer, Colloquium: Cavity-enhanced quantum network nodes, Rev. Mod. Phys. 94, 041003 (2022).
  36. W. Luo, L. Cao, Y. Shi, L. Wan, H. Zhang, S. Li, G. Chen, Y. Li, S. Li, Y. Wang, S. Sun, M. F. Karim, H. Cai, L. C. Kwek, and A. Q. Liu, Recent progress in quantum photonic chips for quantum communication and internet, Light: Sci. Appl. 12, 175 (2023).
  37. C. M. Knaut, A. Suleymanzade, Y. C. Wei, D. R. Assumpcao, P. J. Stas, Y. Q. Huan, B. Machielse, E. N. Knall, M. Sutula, G. Baranes, N. Sinclair, C. De-Eknamkul, D. S. Levonian, M. K. Bhaskar, H. Park, M. Lončar, and M. D. Lukin, Entanglement of nanophotonic quantum memory nodes in a telecom network, Nature (London) 629, 573 (2024).
  38. A. Faraon, A. Majumdar, and J. Vučković, Generation of nonclassical states of light via photon blockade in optical nanocavities, Phys. Rev. A 81, 033838 (2010).
  39. K. M. Birnbaum, A. Boca, R. Miller, A. D. Boozer, T. E. Northup, and H. J. Kimble, Photon blockade in an optical cavity with one trapped atom, Nature (London) 436, 87 (2005).
  40. J. M. Fink, L. Steffen, P. Studer, L. S. Bishop, M. Baur, R. Bianchetti, D. Bozyigit, C. Lang, S. Filipp, P. J. Leek, and A. Wallraff, Quantum-to-classical transition in cavity quantum electrodynamics, Phys. Rev. Lett. 105, 163601 (2010).
  41. K. Srinivasan and O. Painter, Linear and nonlinear optical spectroscopy of a strongly coupled microdisk–quantum dot system, Nature (London) 450, 862 (2007).
  42. L. Stern, B. Desiatov, I. Goykhman, and U. Levy, Nanoscale light–matter interactions in atomic cladding waveguides, Nat. Commun. 4, 1548 (2013).
  43. S. Knappe, V. Shah, P. D. D. Schwindt, L. Hollberg, J. Kitching, L.-A. Liew, and J. Moreland, A microfabricated atomic clock, Appl. Phys. Lett. 85, 1460 (2004).
  44. X. Cheng, Dataset and analysis code for “Collective strong coupling of thermal atoms to integrated microring resonators” [Data set], Zenodo, 2026, https://doi.org/10.5281/zenodo.19457098.
  45. D. K. Venkatachalam, J. E. Bradby, M. N. Saleh, S. Ruffell, and R. G. Elliman, Nanomechanical properties of sputter-deposited HfO2 and HfxSi1−xO2 thin films, J. Appl. Phys. 110, 043527 (2011).
  46. J. Q. Grim, A. S. Bracker, M. Zalalutdinov, S. G. Carter, A. C. Kozen, M. Kim, C. S. Kim, J. T. Mlack, M. Yakes, B. Lee, and D. Gammon, Scalable in operando strain tuning in nanophotonic waveguides enabling three-quantum-dot superradiance, Nat. Mater. 18, 963 (2019).
  47. J. Holzgrafe, N. Sinclair, D. Zhu, A. Shams-Ansari, M. Colangelo, Y. Hu, M. Zhang, K. K. Berggren, and M. Lončar, Cavity electro-optics in thin-film lithium niobate for efficient microwave-to-optical transduction, Optica 7, 1714 (2020).
  48. D. Walls and G. J. Milburn, Quantum Optics (Springer, Berlin, 2007), pp. 231–246.
  49. T. J. Killian, Thermionic phenomena caused by vapors of rubidium and potassium, Phys. Rev. 27, 578 (1926).
  50. S. Zou, D. J. Morin, C. Weaver, Z. Armanfard, J. Muschell, A. I. Nahlawi, and B. Saam, Collisional electron paramagnetic resonance frequency shifts in Cs-Rb-Xe mixtures, Phys. Rev. A 106, 012801 (2022).
  51. D. A. Steck, Rubidium 85 D line data, revision 2.3.4, 8 August 2025, https://steck.us/alkalidata/ .
  52. C. W. Gardiner and M. J. Collett, Input and output in damped quantum systems: Quantum stochastic differential equations and the master equation, Phys. Rev. A 31, 3761 (1985).

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Phys. Rev. Research 8, 043063– Published 16 October, 2026
  • Received 7 April 2026
  • Accepted 18 September 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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