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ABSTRACT An optical cavity enhances the interaction between atoms and light, and the rate of coherent atom–photon coupling can be made larger than all decoherence rates of the system. For

single atoms, this ‘strong coupling regime’ of cavity quantum electrodynamics1,2 has been the subject of many experimental advances. Efforts have been made to control the coupling rate by

trapping3,4 the atom and cooling5,6 it towards the motional ground state; the latter has been achieved in one dimension so far5. For systems of many atoms, the three-dimensional ground state

of motion is routinely achieved7 in atomic Bose–Einstein condensates (BECs). Although experiments combining BECs and optical cavities have been reported recently8,9, coupling BECs to

cavities that are in the strong-coupling regime for single atoms has remained an elusive goal. Here we report such an experiment, made possible by combining a fibre-based cavity10 with

atom-chip technology11. This enables single-atom cavity quantum electrodynamics experiments with a simplified set-up and realizes the situation of many atoms in a cavity, each of which is

identically and strongly coupled to the cavity mode12. Moreover, the BEC can be positioned deterministically anywhere within the cavity and localized entirely within a single antinode of the

standing-wave cavity field; we demonstrate that this gives rise to a controlled, tunable coupling rate. We study the heating rate caused by a cavity transmission measurement as a function

of the coupling rate and find no measurable heating for strongly coupled BECs. The spectrum of the coupled atoms–cavity system, which we map out over a wide range of atom numbers and

cavity–atom detunings, shows vacuum Rabi splittings exceeding 20 gigahertz, as well as an unpredicted additional splitting, which we attribute to the atomic hyperfine structure. We

anticipate that the system will be suitable as a light–matter quantum interface for quantum information13. Access through your institution Buy or subscribe This is a preview of subscription

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FACILITATED BY AN OPTICAL WAVEGUIDE Article Open access 20 October 2020 OPTOMECHANICALLY INDUCED GAIN USING A TRAPPED INTERACTING BOSE-EINSTEIN CONDENSATE Article Open access 04 March 2023

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Scholar  Download references ACKNOWLEDGEMENTS We thank J. Hare and F. Orucevic for support in producing the fibre mirror surfaces, and F. Gerbier for the calculation of condensate size in

the crossover regime. We acknowledge discussions with Y. Castin and J. Dalibard about atom–light interaction in BECs, as well as with T. W. Hänsch, I. Cirac, P. Treutlein and R. Long. This

work was supported by a European Young Investigator Award (EURYI), a Chaire d’Excellence of the French Ministry for Research, and by the EU (‘Atom Chips’ Research Training Network and

‘SCALA’ Integrated Programme). The Atom Chip team at Laboratoire Kastler Brossel is part of the Institut Francilien de Recherche sur les Atomes Froids (IFRAF). AUTHOR INFORMATION Author

notes * Felix Linke Present address: Present address: BMW Group, Abt. Instrumentierung und Displays, Knorrstr. 147, D-80788 München, Germany., * Yves Colombe and Tilo Steinmetz: These

authors contributed equally to this work. AUTHORS AND AFFILIATIONS * Laboratoire Kastler Brossel, ENS/UPMC-Paris 6/CNRS, 24 rue Lhomond, 75005 Paris, France , Yves Colombe, Tilo Steinmetz, 

Guilhem Dubois, Felix Linke & Jakob Reichel * Max-Planck-Institut für Quantenoptik/LMU, Schellingstr. 4, 80799 München, Germany , Tilo Steinmetz & David Hunger Authors * Yves Colombe

View author publications You can also search for this author inPubMed Google Scholar * Tilo Steinmetz View author publications You can also search for this author inPubMed Google Scholar *

Guilhem Dubois View author publications You can also search for this author inPubMed Google Scholar * Felix Linke View author publications You can also search for this author inPubMed Google

Scholar * David Hunger View author publications You can also search for this author inPubMed Google Scholar * Jakob Reichel View author publications You can also search for this author

inPubMed Google Scholar CORRESPONDING AUTHOR Correspondence to Jakob Reichel. ETHICS DECLARATIONS COMPETING INTERESTS The authors declare no competing financial interests. SUPPLEMENTARY

INFORMATION SUPPLEMENTARY NOTES This file contains Supplementary Notes with additional information on collective atom-field interaction and describes two models that we refer to in the

letter: the multilevel coupling model that predicts an anticrossing in the vacuum-Rabi spectrum, and the momentum-diffusion model for cavity field-induced heating of the atom cloud. (PDF 616

kb) RIGHTS AND PERMISSIONS Reprints and permissions ABOUT THIS ARTICLE CITE THIS ARTICLE Colombe, Y., Steinmetz, T., Dubois, G. _et al._ Strong atom–field coupling for Bose–Einstein

condensates in an optical cavity on a chip. _Nature_ 450, 272–276 (2007). https://doi.org/10.1038/nature06331 Download citation * Received: 01 June 2007 * Accepted: 26 September 2007 * Issue

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