Nature volume 588, pages 414–418 (2020)Cite this article
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State-of-the-art atomic clocks are based on the precise detection of the energy difference between two atomic levels, which is measured in terms of the quantum phase accumulated over a given time interval1,2,3,4. The stability of optical-lattice clocks (OLCs) is limited both by the interrupted interrogation of the atomic system by the local-oscillator laser (Dick noise5) and by the standard quantum limit (SQL) that arises from the quantum noise associated with discrete measurement outcomes. Although schemes for removing the Dick noise have been recently proposed and implemented4,6,7,8, performance beyond the SQL by engineering quantum correlations (entanglement) between atoms9,10,11,12,13,14,15,16,17,18,19,20 has been demonstrated only in proof-of-principle experiments with microwave clocks of limited stability. The generation of entanglement on an optical-clock transition and operation of an OLC beyond the SQL represent important goals in quantum metrology, but have not yet been demonstrated experimentally16. Here we report the creation of a many-atom entangled state on an OLC transition, and use it to demonstrate a Ramsey sequence with an Allan deviation below the SQL after subtraction of the local-oscillator noise. We achieve a metrological gain of \(4.{4}_{-0.4}^{+0.6}\) decibels over the SQL by using an ensemble consisting of a few hundred ytterbium-171 atoms, corresponding to a reduction of the averaging time by a factor of 2.8 ± 0.3. Our results are currently limited by the phase noise of the local oscillator and Dick noise, but demonstrate the possible performance improvement in state-of-the-art OLCs1,2,3,4 through the use of entanglement. This will enable further advances in timekeeping precision and accuracy, with many scientific and technological applications, including precision tests of the fundamental laws of physics21,22,23, geodesy24,25,26 and gravitational-wave detection27.
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We thank H. Katori, W. Ketterle, A. Ludlow, M. Lukin, J. Ramette, G. Roati, A. Urvoy, Z. Vendeiro and J. Ye for discussions. This work was supported by NSF, DARPA, ONR and the NSF Center for Ultracold Atoms (CUA). S.C. and A.F.A. acknowledge support from the Swiss National Science Foundation (SNSF). B.B. acknowledges support from the National Science and Engineering Research Council of Canada.
Author information Author notesBoris Braverman
Present address: Department of Physics and Max Planck Centre for Extreme and Quantum Photonics, University of Ottawa, Ottawa, Ontario, Canada
Akio Kawasaki
Present address: W. W. Hansen Experimental Physics Laboratory and Department of Physics, Stanford University, Stanford, CA, USA
These authors contributed equally: Edwin Pedrozo-Peñafiel, Simone Colombo, Chi Shu
Department of Physics, MIT-Harvard Center for Ultracold Atoms and Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA, USA
Edwin Pedrozo-Peñafiel, Simone Colombo, Chi Shu, Albert F. Adiyatullin, Zeyang Li, Enrique Mendez, Boris Braverman, Akio Kawasaki, Daisuke Akamatsu, Yanhong Xiao & Vladan Vuletić
Department of Physics, Harvard University, Cambridge, MA, USA
Chi Shu
National Metrology Institute of Japan (NMIJ), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan
Daisuke Akamatsu
State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, and Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, China
Yanhong Xiao
A.K., B.B., C.S., E.P.-P., S.C., A.F.A., Z.L., E.M. and V.V. contributed to the building of the experiment. E.P.-P., S.C. and C.S. led the experimental efforts and simulations. S.C., A.F.A., C.S. and E.P.-P. contributed to the data analysis. V.V. conceived and supervised the experiment. S.C. and V.V. wrote the manuscript. All authors discussed the experiment implementation and results and contributed to the manuscript.
Corresponding authorCorrespondence to Vladan Vuletić.
Ethics declarations Competing interestsThe authors declare no competing interests.
Additional informationPeer review information Nature thanks the anonymous reviewer(s) for their contribution to the peer review of this work. Peer reviewer reports are available.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Supplementary information About this article Cite this articlePedrozo-Peñafiel, E., Colombo, S., Shu, C. et al. Entanglement on an optical atomic-clock transition. Nature 588, 414–418 (2020). https://doi.org/10.1038/s41586-020-3006-1
Received: 12 June 2020
Accepted: 21 October 2020
Published: 16 December 2020
Issue Date: 17 December 2020
DOI: https://doi.org/10.1038/s41586-020-3006-1
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