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Experimental realization of a one-atom laser in the regime of strong coupling

Abstract

Conventional lasers (from table-top systems to microscopic devices) typically operate in the so-called weak-coupling regime, involving large numbers of atoms and photons; individual quanta have a negligible impact on the system dynamics. However, this is no longer the case when the system approaches the regime of strong coupling for which the number of atoms and photons can become quite small. Indeed, the lasing properties of a single atom in a resonant cavity have been extensively investigated theoretically1,2,3,4,5,6,7,8,9,10,11. Here we report the experimental realization of a one-atom laser operated in the regime of strong coupling. We exploit recent advances12 in cavity quantum electrodynamics that allow one atom to be isolated in an optical cavity in a regime for which one photon is sufficient to saturate the atomic transition. The observed characteristics of the atom–cavity system are qualitatively different from those of the familiar many-atom case. Specifically, our measurements of the intracavity photon number versus pump intensity indicate that there is no threshold for lasing, and we infer that the output flux from the cavity mode exceeds that from atomic fluorescence by more than tenfold. Observations of the second-order intensity correlation function demonstrate that our one-atom laser generates manifestly quantum (nonclassical) light, typified by photon anti-bunching and sub-poissonian photon statistics.

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Figure 1: A simplified schematic of the experiment.
Figure 2: Total counting rate R recorded by detectors D1,2 is displayed as a function of time for two separate trapped atoms, with the counts summed over 5-ms bins.
Figure 3: The intracavity photon number ± σn, inferred from measurements as in Fig. 2, is plotted as a function of dimensionless pump intensity x ≡ (7/9) (I3/I4) for fixed I4 = 13 over two ranges of pump level x.
Figure 4: The intensity correlation function g(2)(τ) is given for two values of the pump intensity in ad, where b and d show the central features of a and c over a smaller range of τ.

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Acknowledgements

We gratefully acknowledge interactions with K. Birnbaum, C.-W. Chou, A. C. Doherty, L.-M. Duan, T. Lynn, T. Northup, S. Polyakov and D. M. Stamper-Kurn. This work was supported by the National Science Foundation, by the Caltech MURI Center for Quantum Networks, and by the Office of Naval Research.

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Correspondence to H. J. Kimble.

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McKeever, J., Boca, A., Boozer, A. et al. Experimental realization of a one-atom laser in the regime of strong coupling. Nature 425, 268–271 (2003). https://doi.org/10.1038/nature01974

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