Cavity QED with Strong Coupling — Toward the Deterministic Control of Quantum Dynamics

Abstract

Many of the current efforts to control the dynamics of individual quantum systems take place within the setting of cavity quantum electrodynamics (QED). The coupling of an atomic dipole to the mode of an optical resonator has historically produced important quantum effects in the regime of weak coupling between dipole and cavity mode; more recent experiments access the regime of strong coupling and begin to enable control of the quantum states of single atoms and single-photon fields through a coherent coupling that exceeds dissipa-tive rates in the system. We briefly review the historicl path to strong coupling and the variety of experiments involving single-quantum cavity QED. Current achievements and future challenges are illustrated through further discussion of two ongoing experiments in out group: one pursuing quantum feedback to trap single atoms in a cavity mode with single photons, the other building capability for quantum logic by using a FORT to hold atoms within a cavity mode. [Note that the presentation on which this paper is based can be accessed at 1 Brief Overview of Cavity QED Cavity quantum electrodynamics (QED) provides the setting for a wide variety of techniques for the control of individual quantum systems. Numerous protocols exploit the coherent interaction between an atomic dipole and the mode of an optical resonator to achieve deterministic control of both atomic states and states of the light field[l]. Such observation and control of individual quanta are crucial in the developing field of quantum information science; strongly-coupled cavity QED systems are uniquely suited for the implementation of many proposals, for example in the areas of quantum networks and communication[2]. Contemporary experiments in cavity QED build on a rich history of work on the coupling of atomic dipoles to the electromagnetic field in the presence of boundaries or materials which alter the structure of the quantized field. A diverse body of research has investigated changes in atomic radiative processes caused by the presence of a boundary[3]; for example, boundary-induced atomic level shifts form the basis of the Casimir effect[4] and numerous other phenomena[5]. Examples abound of experiments in which these effects occur, either as the primary observation or as important corrections to be taken into account[6]. In the special case of an atom placed inside the mode volume of an optical resonator or cavity, the cavity geometry defines single isolated modes ofthe radiation field that can interact coherently with the atomic dipole. The dipole-field coupling is given by Hint = ng(O'+a + O'_a t), where O'± are dipole raising and lowering operators, (a, at) are field Coherence and Quantum Optics VIII Edited by Bigelow et aI.