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1IntroductionState-of-the-art technologies that enable control and measurement of quantum systems that involve the behavior of photons and atoms is considered a required element to establish quantum node technology, which should perform optimum quantum control of the optical signals that come and go through the trunk lines of an information network. e ionic-quantum system — brought to a quiescent state through laser cooling and held in an ion trap — exhibits some distinguished characteristics including: measurable and controllable on individual quantum state levels using a laser and other tools, and controllable on all quantum state levels through the interaction of trap potential and coulomb potential [1]. It is also known that the quantum state of a photon and ion can be mutually converted by coupling them with the quantum eld inside an optical cavity [2]. ese characteristics make ionic-quantum sys-tems the objective of studies in broad areas such as quan-tum computers [1], quantum simulators [3], and optical frequency standards [4], as well as in the application as a quantum node. NICT has undertaken research and devel-opment on state-of-the-art technology to control and measure calcium (40Ca+) and indium (115In+) ions aiming at the application for optical frequency standards. is report outlines the process and results of these research undertak-ings.e characteristics of the laser-cooled ionic quantum system in an ion trap are summarized as below (for detailed descriptions, see reference [1]). e linear ion trap is the device most commonly used to accumulate multiple ions (the construction is shown in Fig. 1(a)). is device, placed in a high-vacuum chamber and driven by applying alterna-tive and direct electric elds of several hundred volts, is capable of trapping ions in the vicinity of its center sur-rounded by electrodes. Because the ion trap itself does not possess a feature to cool ions, a technique called laser cooling is concurrently used. e ion, when brought into a quiescent state, is a subject of direct observation: uores-cent photons emitted from the ion can be captured by a feeble light imaging device (Image-intensied CCD:ICCD). Figure 1(b) shows a uorescence image of laser-cooled Ca+ ions that are aligned in the trap. is state — i.e. the ions are completely isolated from the environment and localized in the region below the wavelength of light — can be sustained for a prolonged period, even for several days, enabling observation and control on an individual quantum state basis. Applications of ionic quantum systems, typi-cally a quantum node, is based on these characteristics.Section 2 of this report outlines research and develop-ment on coherent light sources, which constitute a basic tool to realize state-of-the-art control and measurement of ionic quantum systems. Section 3 describes research and development on sympathetic cooling, which plays an im-portant role in kinematic control of In+ that dees easy laser cooling. Section 4 outlines how we implemented In+ clock transition frequency measurement based on the re-sults of our research and development. In Section 5, we summarize the results from our research and development and take a look at future perspectives.FiF1　(a) Linear ion trap (b) image of laser cooled calcium ions(a)(b)4-4 Quantum State Engineering of Trapped IonsKazuhiro HAYASAKA, Kentaro WAKUI, Nozomi OHTSUBO, Ying LI, Kensuke MATSUBARA, and Tetsuya IDOMeasurement and control on quantum systems are of fundamental importance for implementing the quantum node technologies. We report on research and development activities with the quantum systems consisting of trapped ions, and on the application to an optical frequency standard.714 Quantum Node Technology