Observation of the Vacuum Rabi Spectrum for One Trapped Atom

Abstract

The transmission spectrum for one atom strongly coupled to the field of a high finesse optical resonator is observed to exhibit a clearly resolved vacuum-Rabi splitting characteristic of the normal modes in the eigenvalue spectrum of the atom-cavity system. A new Raman scheme for cooling atomic motion along the cavity axis enables a complete spectrum to be recorded for an individual atom trapped within the cavity mode, in contrast to all previous measurements in cavity QED that have required averaging over many atoms.A cornerstone of optical physics is the interaction of a single two-level atom with the electromagnetic field of a high quality resonator. Of particular importance is the regime of strong coupling, for which the frequency scale g associated with reversible evolution for the atom-cavity system exceeds the rates (γ, κ) for irreversible decay of atom and cavity field, respectively [1]. In the domain of strong coupling, a photon emitted by the atom into the cavity mode is likely to be repeatedly absorbed and reemitted at the single-quantum Rabi frequency 2g before being irreversibly lost into the environment. This oscillatory exchange of excitation between atom and cavity field results from a normal mode splitting in the eigenvalue spectrum of the atom-cavity system [2] which is manifest in emission [3] and absorption [4] spectra, and has been dubbed the vacuum-Rabi splitting [3].Strong coupling in cavity QED as evidenced by the vacuum-Rabi splitting provides enabling capabilities for quantum information science, including for the implementation of scalable quantum computation [5,6], for the realization of distributed quantum networks [7,8], and more generally, for the study of open quantum systems [9]. Against this backdrop, experiments in cavity QED have made great strides over the past two decades to achieve strong coupling [10]. The vacuum-Rabi splitting for single intracavity atoms has been observed with atomic beams in both the optical [11,12,13] and microwave regimes [14]. The combination of laser cooled atoms and large coherent coupling has enabled single atomic trajectories to be monitored in real time with high signal-to-noise ratio, so that the vacuum-Rabi spectrum could be obtained from atomic transit signals produced by single atoms [15]. A significant advance has been the trapping of individual atoms in an optical cavity in a regime of strong coupling [16,17], with the vacuum-Rabi splitting first evidenced for single trapped atoms in Ref.[16] and the entire transmission spectra recorded in Ref. [18].Without exception these prior single atom experiments related to the vacuum-Rabi splitting in cavity QED [11,12,13,14,15,16,17,18] have required averaging over trials with many atoms to obtain quantitative spec- tral information, even if individual trials involved only single atoms (e.g., 10 5 atoms were required to obtain a spectrum in Ref. [14] and > 10 3 atoms were needed in Ref. [18]). By contrast, the implementation of complex algorithms in quantum information science requires the capabili...

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