Strong cavity-mediated coupling of a micromechanical membrane to a single atom

Recent experiments with micro- and nanomechanical oscillators coupled to the optical field in a cavity are approaching the regime where quantum effects dominate. In light of this progress, the question arises to what extent the quantized motion of a mesoscopic mechanical system can be coherently coupled to a microscopic object, the ultimate challenge being strong coupling to the motion of a single atom.

In a theory paper [1], we show that strong coupling between a single atom and a micromechanical membrane can be achieved with the help of a high-finesse optical cavity. The quantized light field in the laser-driven cavity mediates the coupling between the motion of the atom and the membrane. Figure 1 illustrates the coupling mechanism.

Figure 1: a) Schematic setup with atom and membrane inside the cavity. b) Two cavity modes are driven by two lasers with red and blue detuning, respectively. c) Both lasers act as red-detuned optical lattices for the atom. d) Atom, membrane, and cavity field in equilibrium. e) A small displacement of the membrane shifts the cavity resonances, resulting in a spatial shift of the trap potential for the atom. This leads to an effective linear atom-membrane coupling.

We consider a membrane placed in a laser-driven high-finesse cavity representing the opto-mechanical system with radiation pressure coupling. In this setup the motion of the membrane manifests itself as a dynamic detuning of cavity modes. For a cavity mode driven by a detuned laser this translates into a variation of the intensity of the intracavity light field. In addition, we assume that this intracavity field provides an optical lattice as a trap for a single atom. Thus for the setup of Fig. 1, the motion of the membrane will be coupled via the dynamics of the optical trap to the motion of the atom, and vice versa. This coupling is strongly enhanced by the cavity finesse which is a key ingredient in achieving the strong coupling regime.

Remarkably, in this setup a coherent coupling for single-atom and membrane exceeding the dissipative rates by a factor of ten is within reach for near-future experimental parameters. If a small ensemble of N atoms is trapped inside the cavity, the coupling is further enhanced by a factor sqrt(N). Entering the strong coupling regime provides a quantum interface allowing the coherent transfer of quantum states between the mechanical oscillator and the atoms, opening the door to coherent manipulation, preparation and measurement of micromechanical objects via the well-developed tools of atomic physics.

Reference and collaboration

[1] K. Hammerer et al., Phys. Rev. Lett. 103, 063005 (2009), see our list of publications. The paper is the result of a collaboration with the groups of P. Zoller (Innsbruck), F. Marquardt (Munich), J. Kimble (Caltech), and J. Ye (Boulder).