A MEMS-based device for trapped-ion quantum network nodes

As we move from fundamental research on quantum physics toward a new era of quantum technologies, efforts are underway to translate proof-of-principle laboratory experiments into compact, scalable devices. Within this project, we focus on constructing a scalable quantum interface between trapped ions one of the leading platforms for quantum technologies and single photons. Such interfaces are expected to be an integral part of future quantum networks. We will test an ion trap based on microelectromechanical systems (MEMS), which are devices with very small moving parts, based on fabrication technologies from the semiconductor industry. These MEMS technologies will allow us to integrate two optical fibers into the ion trap and to adjust the position of each fiber. Each fiber will be coated with a highly reflective mirror, and by placing the fibers opposite to one another, we can form a so-called optical resonator. The resonator will allows us to collect single particles of light, known as photons, from a single ionized calcium atom. It will also allow us to deliver photons efficiently to the ion and to control the quantum-mechanical interactions between ions and photons. The key question we will explore is whether this miniaturized device can compete with the current performance of much bulkier, hand-built laboratory setups. If so, it may enable quantum communication in between long-distance networks of ions, allowing us to achieve tasks that are not possible over todays communication networks. With international collaborators, we have recently conducted a feasibility study of the proposed device, with promising results. This project now allows us to test the device in practice. In the process, we will develop new techniques that are broadly relevant for quantum technologies, including new laser machining methods for fiber resonators and the integration of waveguides with ion traps.

As we move from fundamental research on quantum physics toward a new era of quantum technologies, efforts are underway to translate proof-of-principle laboratory experiments into compact, scalable devices. Within this project, we focused on constructing a scalable quantum interface for linking up trapped-ion quantum processors. Trapped ions are one of the leading platforms for quantum technologies, and such scalable interfaces are expected to be an integral part of future quantum networks. Here, the basis for the interface is a high-finesse optical resonator, consisting of two highly reflective mirrors, each on the tip of an optical fiber. The resonator is formed by placing the fibers opposite to one another and allows us to collect single particles of light, known as photons, from a single ionized calcium atom. It also allows us to deliver photons efficiently to the ion and to control the quantum-mechanical interactions between ions and photons. In collaboration with colleagues at Seoul National University (SNU), we designed an ion trap compatible with microelectromechanical systems (MEMS), which are devices with very small moving parts, based on fabrication technologies from the semiconductor industry. In the future, these MEMS technologies will allow us to integrate the fiber mirrors into the ion trap and to adjust the position of each mirror, in order to align and stabilize the resonator. Our colleagues at SNU fabricated the trap, and we tested the trap's operation in an ultra-high vacuum chamber that we designed and constructed for these experiments. In parallel, the MEMS devices were designed and fabricated at SNU. Due to several challenges in the fabrication processes, we did not have time before the end of the project to integrate the MEMS and fibers with the ion trap. As an intermediate step, we published a research paper on the silicon-based ion-trap chip and how it is protected from semiconductor charging effects. This project represented a crucial first step in testing a device that we proposed in 2019 as a promising approach to scalable quantum interfaces. Furthermore, it has established an ongoing collaboration with experts in semiconductor fabrication, allowing us to work with quantum hardware with complex geometries. As a next step, we plan to construct an optical resonator with the MEMS-actuated fibers and to compare the coupling of ions to this resonator with the current performance of much bulkier, hand-built laboratory setups, in order to understand whether the miniaturized device provides a realistic path forward.