Cavity QED in a molecular ion trap

We propose a class of experiments using rotational states of dipolar molecular ions trapped near an on-chip superconducting microwave cavity. Molecular ions have several advantages over neutral molecules for such cavity quantum electrodynamics experiments. In particular, ions can be loaded easily into deep rf traps and are held independent of their internal state. An analysis of the detection efficiency for, and coherence properties of, the molecular ions is presented. We discuss approaches for manipulating quantum information and performing high-resolution rotational spectroscopy using this system.

Figure 1

(a) Schematic of molecular ions trapped inside an integrated microwave resonator and split-ground ion trap. The inset shows contours of constant electric field magnitude ($\left|\mathcal{E}\right|$) in response to voltages on the two center electrodes. The two center electrodes are used both for trapping and for coupling molecules to the cavity. Electric field contours are colored from low (blue, outer countor) to high (red, inner countor) $\left|\mathcal{E}\right|$. (b) The trapping ($\Sigma$) mode, when driven at ${\Omega }_{\mathrm{rf}}$, forms a dynamically stable minimum between the two electrodes. (c) The coupling ($\delta$) mode is coplanar-stripline with inductive shorts forming a half-wave ($\lambda /2$) microwave cavity at the molecular rotation frequency (${\omega }_{01}~10$ GHz). At the trap location, the $\delta$ mode has a saddle point in $\left|\mathcal{E}\right|$, with a large electric field for coupling to the molecules’ rotational dipole.