| 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 |
During the first part of the fellowship, the focus was on the design of a new type of nonlinear oscillator device. Using an earlier nonlinear oscillator design, we fabricated some initial devices, learning fabrication techniques such as e-beam lithography and shadow evaporation in the process. A workflow for designing new devices was developed, comprising a script-based step for designing new devices, calculating the classical linearized electromagnetic properties of the devices using standard finite-element techniques, and then using black-box quantization theory to predict their full properties including the nonlinearities. These steps are then iterated.
To design a device with low internal losses, we use smooth edges and large capacitive gaps. This is to prevent spots in the devices that exhibit a high electric field, which could cause a strong coupling to two-level fluctuators (TLFs). These TLFs have been shown to contribute to internal losses in such devices, and keeping internal losses low is critical for achieving the superpositions of cat states that are central to this work.
We have opted for a design with a large central island and a single SQUID, rather than a design using a co-planar waveguide resonator terminated with a squid or a lumped-element type design using arrays of junctions. The former type of design has not shown sufficiently low internal loss in previous work, and in the latter the junction arrays can lead to complicated undesired dynamics.
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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
So far, the main work has been to design the KPO devices. As our designs are different from existing Kerr parametric oscillator devices, getting a device with the right parameters took some time. The initial designs turned out to not lead to the right parameters, so a few different shapes had to be tried before we found something that works. The shapes we eventually settled upon are somewhat unconventional, and writing the code to parametrize and generate such devices also took a non-negligible effort.
Now that a device geometry with the correct parameters has been designed, fabrication and testing is expected to start soon.
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| 今後の研究の推進方策 |
First we will start fabricating these devices and test their properties. Depending on the results (mostly the internal quality factor of the device), we might need to iterate the design and fabrication step, or we might proceed straight to the experiments. After initial characterization of the device, we will need to implement Wigner tomography in order to study the superposition of states in the KPO in detail. Depending on the exact characteristics of the experimental devices and the status of the research field at that time, we can then to decide to implement logical gates on the cat states in a single KPO, or perform precise monitoring of the dynamics in the evolution of the cat states. After that, we will design and fabricate more complicated devices. A first candidate is a KPO with tunable coupling to its environment, enabling us to generate high-fidelity cat states with the environment 'switched off'. Another possibility is to couple two KPOs with a tunable coupler, which will enable us to drive both single and two-qubit gates, allowing a proof-of-principle demonstration of the ability to build a quantum computer using KPOs. We can also combine KPOs with conventional superconducting qubits, to use the KPO for parity measurements.
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