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

## Abstract

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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## Data availability

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

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## Acknowledgements

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.

## Author information

Authors

### Contributions

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.

### Corresponding author

Correspondence to Manuel Endres.

## Ethics declarations

### Competing interests

The authors declare no competing interests.

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 information

### Supplementary Information

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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• ### A boost to Rydberg quantum computing

• Wenhui Li

Nature Physics (2020)