| Project/Area Number |
23K26580
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| Project/Area Number (Other) |
23H01887 (2023)
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Multi-year Fund (2024)
Single-year Grants (2023) |
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| Section | 一般 |
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| Review Section |
Basic Section 30020:Optical engineering and photon science-related
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| Research Institution | NTT Basic Research Laboratories |
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Principal Investigator |
徐 学俊 日本電信電話株式会社NTT物性科学基礎研究所, フロンティア機能物性研究部, 主任研究員 (80593334)
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| Co-Investigator(Kenkyū-buntansha) |
石澤 淳 日本大学, 生産工学部, 教授 (30393797)
俵 毅彦 日本大学, 工学部, 教授 (40393798)
太田 竜一 日本電信電話株式会社NTT物性科学基礎研究所, フロンティア機能物性研究部, 主任研究員 (90774894)
稲葉 智宏 日本電信電話株式会社NTT物性科学基礎研究所, フロンティア機能物性研究部, 研究主任 (90839119)
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| Project Period (FY) |
2023-04-01 – 2026-03-31
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| Project Status |
Granted (Fiscal Year 2024)
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| Budget Amount *help |
¥18,460,000 (Direct Cost: ¥14,200,000、Indirect Cost: ¥4,260,000)
Fiscal Year 2025: ¥4,940,000 (Direct Cost: ¥3,800,000、Indirect Cost: ¥1,140,000)
Fiscal Year 2024: ¥4,030,000 (Direct Cost: ¥3,100,000、Indirect Cost: ¥930,000)
Fiscal Year 2023: ¥9,490,000 (Direct Cost: ¥7,300,000、Indirect Cost: ¥2,190,000)
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| Keywords | Rare-earth ion / Nuclear spin / Photonic nanocavity / Rare earth ion / Silicon photonics / Waveguide / Photonic crystal cavity |
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| Outline of Research at the Start |
In this project, an on-chip nuclear spin qubit platform with long coherence time and direct compatibility with telecommunication photons will be developed based on individual isotope-purified 167Er3+ ions doped in crystal host materials integrated on Si substrate, in order to implement single ion based quantum repeaters in the telecommunication band. First, single 167Er3+ ions will be optically addressed by using photonic crystal nanocavities. Then, initialization, control and readout quantum states of individual 167Er3+ nuclear spin qubits will be demonstrated.
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| Outline of Annual Research Achievements |
Single crystal 167Er-doped rare-earth oxide (REO, Gd2O3 and CeO2) thin films were grown on silicon-on-insulator (SOI) substrates. Crystal quality and optical properties were largely improved through incorporating undoped REO buffer and post-growth annealing. At low doping concentrations, fluorescence linewidth narrowing was observed, indicating the possibility of coherent operation of Er3+ ions. SiN/REO/SOI waveguides with low propagation loss (<0.5 dB/cm) and large optical confinement factors (>40%) were demonstrated, with which 167Er3+ absorption in centimeter long waveguides with diluted doping (~160 ppm) and fluorescence from trace amount (<1 ppm) of Er were observed. These are very important steps towards single ion detection. Waveguide-based microring resonators with high Q-factors on the order of 1E4 were also demonstrated, with significantly enhanced light absorption and emission observed. These high-performance photonic devices will be used to further investigate the coherent properties of 167Er3+ ions. Based on the same multilayer stack, photonic crystal nanobeam cavities with high Q-factor (>2500) and small mode volume (~ 7.6 μm3) were designed, indicating a Purcell factors approaching 100. Through further optimization, larger Purcell factors aiming for single ion detection will be expected. In order to develop quantum control technique for 167Er3+ ions, 167Er3+:Y2SiO5 bulk crystal was also investigated. We demonstrated atomic frequency comb quantum memory operation with high efficiency of 16.7% and verified faithful storage of optical time-bin pulses.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
High quality materials and devices are two most important prerequisites for the ultimate goal of the project: optical addressing of single 167Er3+ ions. For the material side, in the first year of this project, we have successfully grown high quality 167Er-doped Gd2O3 and CeO2 thin films on Si substrates with excellent optical properties. For the device side, we have successfully demonstrated low loss photonic waveguides and microring resonators with large confinement factors and designed photonic nanocavities with high Q-factor and small mode volume. We have also successfully observed 167Er3+ absorption in centimeter long waveguides with diluted doping (~160 ppm) and fluorescence from trace amount (<1 ppm) of Er by using these devices. These results lay a solid ground for the next step of project: measurement of coherent properties of 167Er3+, demonstration of photonic nanocavities with large Purcell factors and optical addressing of single ions. Moreover, to develop spectroscopic technique for controlling quantum states of 167Er3+ ions, as a test bed, we have also investigated the properties of 167Er3+:Y2SiO5 bulk crystals. The developed techniques of population initialization, atomic frequency comb preparation and time-bin pulse storage will be beneficial for the goal of manipulation of quantum states of individual 167Er3+ nuclear spin qubits.
Based on these achievements, we therefore think the project is generally progressing well as planned.
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| Strategy for Future Research Activity |
(1) Optical and spin properties of 167Er3+ ions, including hyperfine level structure, optical and spin coherence times and Λ-like three level system, will be characterized by using waveguide and microresonator structures. For this purpose, milli-Kelvin optical waveguide measurement system will be built in a dilution refrigerator.
(2) The designed photonic nanocavities will be further optimized to increase Purcell factors, and then fabricated by optimized process. Other novel device structures such as metasurfaces will also be investigated as an alternative device candidate.
(3) Photoluminescence excitation spectroscopy will be used to address 167Er3+ ions. Existence of individual ions can be observed as discrete absorption lines. The second-correlation g(2) of emitted photons will be measured for further confirmation of single ions. Magnetic field dependence will be characterized to distinguish 167Er3+ with other isotopes.
(4) On-chip microwave coplanar waveguides or resonators will be designed and fabricated together with photonic nanocavities to spin transitions in 167Er3+ ions. Techniques of cryogenic optical and microwave package of chips will also be developed.
(5) State initialization, control, and readout of individual 167Er3+ ions will be performed. Optical pumping will be used for state initialization and readout of nuclear spin state will be performed by analyzing the statistics of emitted photons. Finally, Rabi oscillation between qubit levels will be measured by applying microwave excitations, thus demonstrating control of qubit state.
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