Strong coupling of a single ion to an optical cavity

We report a novel miniature Paul ion trap design with an integrated optical fibre cavity which can serve as a building block for a fibre-linked quantum network. In such cavity quantum electrodynamic set-ups, the optimal... [ view full abstract ]

We report a novel miniature Paul ion trap design with an integrated optical fibre cavity which can serve as a building block for a fibre-linked quantum network. In such cavity quantum electrodynamic set-ups, the optimal coupling of the ions to the cavity mode is of vital importance and this is achieved by moving the ion relative to the cavity mode. The trap presented herein features an endcap-style design complemented with extra electrodes on which additional radiofrequency voltages are applied to fully control the pseudopotential minimum in three dimensions (fig.1). Based on the setup presented in this work we achieve a coherent ion-cavity coupling of g0= 2π×15.0 MHz greater than both atomic and cavity decay rates of γ= 2π×11.5 MHz and κ= 2π×4.0 MHz respectively.

By applying additional rf voltage to the side electrodes we can move the ion radially. By combining this with a dc voltage in the axial direction, we position the ion in the cavity centre at an antinode of the standing wave, where it is maximally coupled to the cavity. If we detune our 397nm cooling laser (fig.2) from the atomic transition and scan the cavity we would expect to see the linecentre of the cavity scan the same frequency away from the atomic transition. What we observe is that depending on the strength of the coupling of the ion with the cavity there is a shift from the expected linecentre value. This result was confirmed by running a simulation of the system. We repeat the measurement over a range of detunings and then we fit the results using our simulation to extract the strength of the ion-cavity coupling (fig.3). The extracted ion-cavity coupling lies in the strong coupling regime.
Here we demonstrate a key feature for a scalable QIP system using trapped ions by coupling a single ion to an optical cavity and operating them in strong coupling regime for the first time.