| 研究課題/領域番号 |
25420352
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| 研究種目 |
基盤研究(C)
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| 研究機関 | 独立行政法人情報通信研究機構 |
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研究代表者 |
丘 偉 独立行政法人情報通信研究機構, 未来ICT研究所 ナノICT研究室, 研究員 (90535189)
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| 研究期間 (年度) |
2013-04-01 – 2016-03-31
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| キーワード | epitaxial / qubit / CPW / junction / energy relaxation time / superconducting / Josephson |
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| 研究概要 |
Full epitaxial NbN qubits embedded in the NbN coplanar waveguide resonator on a single crystal MgO substrate has been fabricated with SiO2 as the insulation layer for the junction. The device was measured at 30 mK in the Dilution Refrigerator KMX400. NbN resonator show an internal loss of 3.3x10-4. Estimated energy relaxation time T1 of 1 us, agrees well with the measured qubit energy relaxation T1 time.
Systematically characterized the internal losses using epitaxially grown NbN thin film microwave coplanar waveguide resonator on MgO substrate at 300 mK. It showed that both the SiO2 and SiNx insulation materials only plan a limited role of the total loss of the NbN-qubit circuit. It is the MgO substrate that dominates the internal loss of the current NbN-qubit circuit. Initial test of superconducting TiN microwave CPW resonator fabricated on hydrogen-terminated Si substrate showed a significant improvement of internal loss of about 5x10-6.
Future investigation of the internal loss on Si-based superconducting microwave resonator is necessary as well as further exploration the possibility of fabrication high quality Josephson devices on Si substrate.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
2: おおむね順調に進展している
理由
Low critical current density (100 A/cm2) and full epitaxial NbN Josephson junctions on MgO substrate have been fabricated and characterized at the liquid Helium temperature. A qubit circuit consists of such high quality junctions embedded in the NbN coplanar waveguide resonator on a single crystal MgO substrate has been measured at 30 mK in the Dilution Refrigerator.
A SiNx 6 inches target has been installed and the sputtering rate is 2.33 nm/s under current sputtering condition. The initial result of NbN junctions using SiNx as the insulation material showed good quality and low sub-gap leakage current.
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| 今後の研究の推進方策 |
The superconducting microwave coplanar waveguide resonator deposited on the hydrogen-terminated Si substrate has showed a much lower internal loss when compares to the internal loss on a single crystal MgO substrate. This suggests Si substrate is a better candidate for further Josephson junction and superconducting qubit circuit fabrication.
Currently, both SiO2 and SiNx amorphous films are deposited by sputtering and both materials in theory could contribute to the total internal loss of the qubit circuit. Future research will also explore the possibility of fabrication vacuum-gap junctions by removing the SiO2 layer by hydrogen fluoride etch process.
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| 次年度の研究費の使用計画 |
The incurred amount from last fiscal year was due to the shorter than expected experiment time of running dilution refrigerator, therefore the less cost of liquid Helium.
The incurred amount will be used to cover the extra cost of liquid Helium as the unit cost of liquid Helium will be increased from the next fiscal year.
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