Design of a fiber cavity ion trap for a high-efficiency and high-rate quantum network node

Figure  1.  (a) Schematic diagram of the fiber cavity ion trap system. The fiber cavity ion trap is placed in the middle of the vacuum chamber. A single $ ^{138}\text{Ba}^{+} $ ion is trapped in the center. The red and blue lines are the modulation lasers. (b) The basic atomic energy level for photon generation.

Figure  2.  Diagram of the fiber cavity ion trap system in vacuum. The fiber electrodes are mounted on a fiber mounting base. This system uses a ceramic circuit board to energize the ion trap. The stainless steel base of the device is composed of two spring-connected parts, and the lower part of the stainless steel base is directly connected to the vacuum chamber through grippers.

Figure  3.  Flow chart for fabricating fiber electrodes. The cut bare fiber undergoes a complete process to form a central light-permeable electrode structure with a gold layer around the cavity surface to shield the charges from the high-reflection film.

Figure  4.  Arrangement of the fiber electrodes in the system. The four side fiber electrodes are grounded by default, and the middle fiber electrodes are applied with the RF electric field.

Figure  5.  Schematic diagram of the interaction between the fiber cavity and the ion. In the presence of an external electric field $E_{{\rm{s}}}\cos(\omega_{{L}}t)$, the single ion interacts with the cavity. In cavity quantum electrodynamics, this interaction can be described using $ (g,\kappa,\gamma) $. There is only a fundamental mode in the cavity and the distribution is affected by the structure of the cavity. Here, $ w_{{\rm{s}},i} \) (\({\rm{s}}={\rm{f}},{\rm{m}}\) and \(i=1,2)$ is the radius of the mode field at each location, $ w_{0} $ is the radius of the waist, $R_{i} \) (\(i=1,2)$ is the radius of curvature (ROC), $ n_{i} \) (\(i=1,2)$ is the refractive index, and $ L $ is the cavity length. At the fiber end face, only the mode field within diameter $ D_{i} \) (\(i=1,2)$ can be reflected by the fiber.

Figure  6.  Variation curves of each coupling with the radius of curvature (ROC) of the left cavity surface $ R_{1} $ when reflectivity $ {\cal{R}}_{1}=99.8\% $, $ {\cal{R}}_{2}=99.98\% $, and the type of fiber is LMA-10 photonic crystal fiber. $ P $ is the overall efficiency in the figure.

Figure  7.  Simulated potential energy. A drive voltage of $ 100 $ V is applied to the RF fiber electrodes. The origin of these figures is the center of the fiber cavity.The curves in (a)–(c) show the potential energy along the $ x $, $ y $, and $ z $ directions through the origin, and each red dashed line represents the result of the fit of the quadratic function. The images in (d)–(f) show the potential energy in terms of different cross-section.

Figure  8.  Schematic diagram of the connection of the stainless steel base. The figure shows the spring arrangement as seen from the side. The stainless steel base uses a total of ten springs, four of which are used to achieve the connection in the vertical direction, and the remaining six springs are used to achieve the connection in the side.

Figure  9.  Simulated resonant modes of the upper part of the system. The solid blue lines in the figure are the original position of the upper part. The darker the color, the greater the displacement of the upper part.