| 研究課題/領域番号 |
18F18364
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| 研究機関 | 国立研究開発法人理化学研究所 |
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研究代表者 |
中村 泰信 国立研究開発法人理化学研究所, 創発物性科学研究センター, チームリーダー (90524083)
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| 研究分担者 |
VAN LOO ARJAN 国立研究開発法人理化学研究所, 創発物性科学研究センター, 外国人特別研究員
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| 研究期間 (年度) |
2018-11-09 – 2021-03-31
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| キーワード | Superconducting qubit / microwave / quantum optics / nonlinear resonator / parametric oscillation |
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| 研究実績の概要 |
After designing KPO devices according to the method outlined in the previous progress report, we fabricated and measured those devices. They did not respond as expected. The discrepancy between the expected and observed behaviour was likely due to a non-negligible geometric inductance in the devices, which can often be ignored in quantum circuits in anything else than thin wires. We verified the existence of this inductance numerically in COMSOL after our lab acquired a fast workstation. We adjusted our design process to use both electrostatic and eigenfrequency simulations to design KPOs with the desired characteristics, and designed the second generation of devices. We have started fabricating these devices.
We also collaborated with S. Kono on his work regarding the breaking of the trade-off in fast control and long lifetime of a superconducting qubit, which is now on the arxiv.
We also collaborated with an axion-search experiment; we designed and fabricated Josephson parametric amplifiers (JPAs) that are being used to improve the signal-to-noise ratio of their experiments. The first JPAs show good gain, but a low bandwidth. We have designed and are fabricating a second generation of JPAs with increased bandwidth.
We analysed the presence of box modes in the sample boxes used in our lab, and found that box modes close to experimental frequencies exist. Our colleagues are designing new sample boxes that remedy this. During the shutdown due to COVID-19, we now work on the theoretical modelling of KPO experiments, and optimize the design of the devices to be fabricated.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
3: やや遅れている
理由
The initial devices not working, and the subsequent redesign have taken more time than anticipated. The new design workflow uses a Comsol eigenfrequency simulation for each candidate design, which is time consuming. After that, we ran into delays due to malfunctioning machines in the fabrication stage: the electron-beam lithography machine was out of commission for about a month, which was quickly followed by the shutdown of the fabrication and laboratory facilities due to COVID-19. As such, we currently cannot proceed with fabrication and experiments, and therefore focus on theoretical modelling and numerical calulations. On the positive side, while the KPO experiments have not progressed as much as we would have liked, the collaborations with colleagues and the axion search group are progressing well.
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| 今後の研究の推進方策 |
Currently we are pursuing numerical modelling of the KPOs and the planned experiments. The next experiments planned, after characterizing the current KPO design, are to generate itinerant microwave cat states on-demand. This proposal relies on a very specific way of driving the KPO. The most challenging thing about this experiment is the verification of the travelling cat state by performing Wigner tomography on the itinerant microwave pulse. We are planning to do so using wide-band Josephson parametric amplifiers and a maximum likelihood state reconstruction as proposed by Lvovsky [1].
At the same time, we are theoretically exploring a few other microwave quantum optics devices we could investigate experimentally once the lab opens back up. To that end we are theoretically investigating waveguide QED with multiple waveguides, a theoretical framework that could lead to many new quantum optics experiments.
[1] A. I. Lvovsky, Iterative maximum-likelihood reconstruction in quantum
homodyne tomography, J. Opt. B Quant. Semicl. Opt. 6, 6 (2004)
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