High-fidelity entanglement and detection of alkaline-earth Rydberg atoms


Trapped neutral atoms have become a prominent platform for quantum science, where entanglement fidelity records have been set using highly excited Rydberg states. However, controlled two-qubit entanglement generation has so far been limited to alkali species, leaving the exploitation of more complex electronic structures as an open frontier that could lead to improved fidelities and fundamentally different applications such as quantum-enhanced optical clocks. Here, we demonstrate a novel approach utilizing the two-valence electron structure of individual alkaline-earth Rydberg atoms. We find fidelities for Rydberg state detection, single-atom Rabi operations and two-atom entanglement that surpass previously published values. Our results pave the way for novel applications, including programmable quantum metrology and hybrid atom–ion systems, and set the stage for alkaline-earth based quantum computing architectures.

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Fig. 1: Population and detection of Rydberg states in non-interacting and interacting configurations.
Fig. 2: Rabi oscillations and auto-ionization.
Fig. 3: Long-time Rabi oscillations for single and blockaded atoms.
Fig. 4: Short-time Rydberg-blockaded Rabi oscillations with tweezers off and on.

Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.


  1. 1.

    Saffman, M., Walker, T. G. & Mølmer, K. Quantum information with Rydberg atoms. Rev. Mod. Phys. 82, 2313–2363 (2010).

    ADS  Google Scholar 

  2. 2.

    Browaeys, A., Barredo, D. & Lahaye, T. Experimental investigations of dipole–dipole interactions between a few Rydberg atoms. J. Phys. B 49, 152001 (2016).

    ADS  Google Scholar 

  3. 3.

    Saffman, M. Quantum computing with atomic qubits and Rydberg interactions: progress and challenges. J. Phys. B 49, 202001 (2016).

    ADS  Google Scholar 

  4. 4.

    Browaeys, A. & Lahaye, T. Many-body physics with individually controlled Rydberg atoms. Nat. Phys. 16, 132–142 (2020).

    Google Scholar 

  5. 5.

    Schauß, P. et al. Crystallization in Ising quantum magnets. Science 347, 1455–1458 (2015).

    ADS  Google Scholar 

  6. 6.

    Labuhn, H. et al. Tunable two-dimensional arrays of single Rydberg atoms for realizing quantum Ising models. Nature 534, 667–670 (2016).

    ADS  Google Scholar 

  7. 7.

    Bernien, H. et al. Probing many-body dynamics on a 51-atom quantum simulator. Nature 551, 579–584 (2017).

    ADS  Google Scholar 

  8. 8.

    Jau, Y. Y., Hankin, A. M., Keating, T., Deutsch, I. H. & Biedermann, G. W. Entangling atomic spins with a Rydberg-dressed spin-flip blockade. Nat. Phys. 12, 71–74 (2016).

    Google Scholar 

  9. 9.

    Levine, H. et al. High-fidelity control and entanglement of Rydberg-atom qubits. Phys. Rev. Lett. 121, 123603 (2018).

    ADS  Google Scholar 

  10. 10.

    Graham, T. M. et al. Rydberg-mediated entanglement in a two-dimensional neutral atom qubit array. Phys. Rev. Lett. 123, 230501 (2019).

    ADS  Google Scholar 

  11. 11.

    Levine, H. et al. Parallel implementation of high-fidelity multiqubit gates with neutral atoms. Phys. Rev. Lett. 123, 170503 (2019).

    ADS  Google Scholar 

  12. 12.

    Omran, A. et al. Generation and manipulation of Schrödinger cat states in Rydberg atom arrays. Science 365, 570–574 (2019).

    ADS  MathSciNet  Google Scholar 

  13. 13.

    Monz, T. et al. 14-qubit entanglement: creation and coherence. Phys. Rev. Lett. 106, 130506 (2011).

    ADS  Google Scholar 

  14. 14.

    Song, C. et al. Generation of multicomponent atomic Schrödinger cat states of up to 20 qubits. Science 365, 574–577 (2019).

    ADS  MathSciNet  Google Scholar 

  15. 15.

    Barredo, D., de Leseleuc, S., Lienhard, V., Lahaye, T. & Browaeys, A. An atom-by-atom assembler of defect-free arbitrary two-dimensional atomic arrays. Science 354, 1021–1023 (2016).

    ADS  Google Scholar 

  16. 16.

    Endres, M. et al. Atom-by-atom assembly of defect-free one-dimensional cold atom arrays. Science 354, 1024–1027 (2016).

    ADS  Google Scholar 

  17. 17.

    Kumar, A., Wu, T. Y., Giraldo, F. & Weiss, D. S. Sorting ultracold atoms in a three-dimensional optical lattice in a realization of Maxwell’s demon. Nature 561, 83–87 (2018).

    ADS  Google Scholar 

  18. 18.

    de Léséleuc, S., Barredo, D., Lienhard, V., Browaeys, A. & Lahaye, T. Analysis of imperfections in the coherent optical excitation of single atoms to Rydberg states. Phys. Rev. A 97, 053803 (2018).

    ADS  Google Scholar 

  19. 19.

    DeSalvo, B. J. et al. Rydberg-blockade effects in Autler–Townes spectra of ultracold strontium. Phys. Rev. A 93, 022709 (2016).

    ADS  Google Scholar 

  20. 20.

    Gaul, C. et al. Resonant Rydberg dressing of alkaline-earth atoms via electromagnetically induced transparency. Phys. Rev. Lett. 116, 243001 (2016).

    ADS  Google Scholar 

  21. 21.

    Lochead, G., Boddy, D., Sadler, D. P., Adams, C. S. & Jones, M. P. A. Number-resolved imaging of excited-state atoms using a scanning autoionization microscope. Phys. Rev. A 87, 053409 (2013).

    ADS  Google Scholar 

  22. 22.

    Norcia, M. A., Young, A. W. & Kaufman, A. M. Microscopic control and detection of ultracold strontium in optical-tweezer arrays. Phys. Rev. X 8, 041054 (2018).

    Google Scholar 

  23. 23.

    Cooper, A. et al. Alkaline-earth atoms in optical tweezers. Phys. Rev. X 8, 041055 (2018).

    Google Scholar 

  24. 24.

    Saskin, S., Wilson, J. T., Grinkemeyer, B. & Thompson, J. D. Narrow-line cooling and imaging of ytterbium atoms in an optical tweezer array. Phys. Rev. Lett. 122, 143002 (2019).

    ADS  Google Scholar 

  25. 25.

    Ludlow, A. D., Boyd, M. M., Ye, J., Peik, E. & Schmidt, P. O. Optical atomic clocks. Rev. Mod. Phys. 87, 637–701 (2015).

    ADS  Google Scholar 

  26. 26.

    Gil, L. I. R., Mukherjee, R., Bridge, E. M., Jones, M. P. A. & Pohl, T. Spin squeezing in a Rydberg lattice clock. Phys. Rev. Lett. 112, 103601 (2014).

    ADS  Google Scholar 

  27. 27.

    Kessler, E. M. et al. Heisenberg-limited atom clocks based on entangled qubits. Phys. Rev. Lett. 112, 190403 (2014).

    ADS  Google Scholar 

  28. 28.

    Kaubruegger, R. et al. Variational spin-squeezing algorithms on programmable quantum sensors. Phys. Rev. Lett. 123, 260505 (2019).

    ADS  Google Scholar 

  29. 29.

    Kómár, P. et al. A quantum network of clocks. Nat. Phys. 10, 582–587 (2014).

    Google Scholar 

  30. 30.

    Daley, A. J., Boyd, M. M., Ye, J. & Zoller, P. Quantum computing with alkaline-earth-metal atoms. Phys. Rev. Lett. 101, 170504 (2008).

    ADS  Google Scholar 

  31. 31.

    Gorshkov, A. V. et al. Alkaline-earth-metal atoms as few-qubit quantum registers. Phys. Rev. Lett. 102, 110503 (2009).

    ADS  Google Scholar 

  32. 32.

    Kaufman, A. M. et al. Entangling two transportable neutral atoms via local spin exchange. Nature 527, 208–211 (2015).

    ADS  Google Scholar 

  33. 33.

    Welte, S., Hacker, B., Daiss, S., Ritter, S. & Rempe, G. Photon-mediated quantum gate between two neutral atoms in an optical cavity. Phys. Rev. X 8, 011018 (2018).

    Google Scholar 

  34. 34.

    Covey, J. P., Madjarov, I. S., Cooper, A. & Endres, M. 2000-times repeated imaging of strontium atoms in clock-magic tweezer arrays. Phys. Rev. Lett. 122, 173201 (2019).

    ADS  Google Scholar 

  35. 35.

    Madjarov, I. S. et al. An atomic-array optical clock with single-atom readout. Phys. Rev. X 9, 041052 (2019).

    Google Scholar 

  36. 36.

    Norcia, M. A. et al. Seconds-scale coherence on an optical clock transition in a tweezer array. Science 366, 93–97 (2019).

    ADS  Google Scholar 

  37. 37.

    Pichler, H., Wang, S. T., Zhou, L., Choi, S. & Lukin, M. D. Quantum optimization for maximum independent set using Rydberg atom arrays. Preprint at http://arxiv.org/abs/1808.10816 (2018).

  38. 38.

    Vaillant, C. L., Jones, M. P. A. & Potvliege, R. M. Long-range Rydberg–Rydberg interactions in calcium, strontium and ytterbium. J. Phys. B 45, 135004 (2012).

    ADS  Google Scholar 

  39. 39.

    Barredo, D. et al. Three-dimensional trapping of individual Rydberg atoms in ponderomotive bottle beam traps. Phys. Rev. Lett. 124, 023201 (2020).

    ADS  Google Scholar 

  40. 40.

    Mukherjee, R., Millen, J., Nath, R., Jones, M. P. A. & Pohl, T. Many-body physics with alkaline-earth Rydberg lattices. J. Phys. B 44, 184010 (2011).

    ADS  Google Scholar 

  41. 41.

    Knill, E. Quantum computing with realistically noisy devices. Nature 434, 39–44 (2005).

    ADS  Google Scholar 

  42. 42.

    Arute, F. et al. Quantum supremacy using a programmable superconducting processor. Nature 574, 505–510 (2019).

    ADS  Google Scholar 

  43. 43.

    Karpa, L., Bylinskii, A., Gangloff, D., Cetina, M. & Vuletić, V. Suppression of ion transport due to long-lived subwavelength localization by an optical lattice. Phys. Rev. Lett. 111, 163002 (2013).

    ADS  Google Scholar 

  44. 44.

    Huber, T., Lambrecht, A., Schmidt, J., Karpa, L. & Schaetz, T. A far-off-resonance optical trap for a Ba+ ion. Nat. Commun. 5, 5587 (2014).

    ADS  Google Scholar 

  45. 45.

    Barredo, D., Lienhard, V., de Léséleuc, S., Lahaye, T. & Browaeys, A. Synthetic three-dimensional atomic structures assembled atom by atom. Nature 561, 79–82 (2018).

    ADS  Google Scholar 

  46. 46.

    Cirac, J. I. & Zoller, P. A scalable quantum computer with ions in an array of microtraps. Nature 404, 579–581 (2000).

    ADS  Google Scholar 

  47. 47.

    Engel, F. et al. Observation of Rydberg blockade induced by a single ion. Phys. Rev. Lett. 121, 193401 (2018).

    ADS  Google Scholar 

  48. 48.

    Mukherjee, R. Charge dynamics of a molecular ion immersed in a Rydberg-dressed atomic lattice gas. Phys. Rev. A 100, 013403 (2019).

    ADS  Google Scholar 

  49. 49.

    Langin, T. K., Gorman, G. M. & Killian, T. C. Laser cooling of ions in a neutral plasma. Science 363, 61–64 (2019).

    ADS  Google Scholar 

  50. 50.

    Wilson, J. et al. Trapped arrays of alkaline earth Rydberg atoms in optical tweezers. Preprint at http://arxiv.org/abs/1912.08754 (2019).

  51. 51.

    Taichenachev, A. et al. Magnetic field-induced spectroscopy of forbidden optical transitions with application to lattice-based optical atomic clocks. Phys. Rev. Lett. 96, 083001 (2006).

    ADS  Google Scholar 

  52. 52.

    Barber, Z. et al. Direct excitation of the forbidden clock transition in neutral 174Yb atoms confined to an optical lattice. Phys. Rev. Lett. 96, 083002 (2006).

    ADS  Google Scholar 

  53. 53.

    Wang, Y., Kumar, A., Wu, T. Y. & Weiss, D. S. Single-qubit gates based on targeted phase shifts in a 3D neutral atom array. Science 352, 1562–1565 (2016).

    ADS  MathSciNet  MATH  Google Scholar 

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We acknowledge discussions with C. Greene and H. Levine as well as funding provided by the Institute for Quantum Information and Matter, an NSF Physics Frontiers Center grant (no. PHY-1733907), an NSF CAREER award (1753386), AFOSR YIP (FA9550-19-1-0044), the Sloan Foundation and F. Blum. Research was carried out at the Jet Propulsion Laboratory and the California Institute of Technology under a contract with the National Aeronautics and Space Administration and funded through the President’s and Director’s Research and Development Fund (PDRDF). J.P.C. acknowledges support from the PMA Prize postdoctoral fellowship and J.C. acknowledges support from the IQIM postdoctoral fellowship. H.P. acknowledges support by the Gordon and Betty Moore Foundation. A.K. acknowledges funding from the Larson SURF fellowship and Caltech Student-Faculty Programs.

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M.E. conceived the idea and initiated the study. I.S.M., J.P.C., A.L.S., J.C., A.C. and V.S. designed and carried out the experiments. I.S.M., J.P.C., A.L.S., J.C., A.K. and H.P. performed theory and simulation work. I.S.M., J.P.C., A.L.S. and J.C. contributed to data analysis. I.S.M., J.P.C., A.L.S., J.C. and M.E. contributed to writing the manuscript and the Supplementary Information. J.P.C., J.R.W. and M.E. supervised and guided this work.

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Correspondence to Manuel Endres.

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Peer review information Nature Physics thanks Markus Hennrich, Thierry Lahaye and Wenhui Li for their contribution to the peer review of this work.

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Supplementary text, Figs. 1–4 and references.

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Madjarov, I.S., Covey, J.P., Shaw, A.L. et al. High-fidelity entanglement and detection of alkaline-earth Rydberg atoms. Nat. Phys. 16, 857–861 (2020). https://doi.org/10.1038/s41567-020-0903-z

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