Real-Time Tracking and Trapping of Single Atoms in Cavity QED

H. J. Kimble, K. Birnbaum, A. C. Doherty, C. J. Hood, T. W. Lynn, H.-C. Nagerl, D. M. Stamper-Kurn, D. W. Vernooy, and J. Ye Norman Bridge Laboratory of Physics 12-33 California Institute of Technology Pasadena, California 91125 Cavity quantum electrodynamics (QED) offers powerful possibilities for the deterministic control of atom-photon interactions quantum by quantum [1]. Indeed, modern experiments in cavity QED have achieved the exceptional circumstance of strong coupling, for which single quanta can profoundly impact the dynamics of the atom-cavity system. The diverse accomplishments of this field set the stage for advances into yet broader frontiers in quantum information science for which cavity QED offers unique advantages, such as the realization of quantum networks by way of multiple atom-cavity systems linked by optical interconnects [2,3]. The primary technical challenge on the road toward such scientific goals is the need to trap and localize atoms within a cavity in a setting suitable for strong coupling. Beginning with the work of Mabuchi et al. [4], several groups have been pursuing the integration of the techniques of laser cooling and trapping with those of cavity quantum electrodynamics (QED). [5-12] Two separate experiments in our group have recently achieved significant milestones in this quest, namely the trapping of single atoms in cavity QED [6,9,10]. Note that these experiments with cold atoms localized over time T achieve g$r > 107r, whereas experiments with conventional atomic beams in cavity QED have gQT ~ TT, with T as the atomic transit time through the cavity mode. In our experiments, the arrival of a single atom into the cavity mode can be monitored with high signal-to-noise ratio in real time by a near resonant field with mean intracavity photon number n < 1. We emphasize that interactions in cavity QED bring an in principle enhancement in the capability to sense atomic motion beyond that which is otherwise possible in free space. Stated quantitatively, the ability to sense atomic motion within an optical cavity by way of the transmitted field can be characterized by the optical information / = a^— = aR£d, which roughly speaking is the maximum possible number of photons that can be collected as signal in time At with efficiency a as an atom transits between a region of optimal coupling #o and one with g(r) (ft, 7),