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| 研究生： |
呂函諭 Lu, Han-Yu |
|---|---|
| 論文名稱： |
探討熱屏蔽塗層對量子位元溫度與讀取保真度的影響 Evaluating the Effect of Shielding on Qubit Temperature and Readout Fidelity |
| 指導教授： |
柯忠廷
Ke, Chung-Ting |
| 口試委員: |
陳啟東
Chen, Chii-Dong 許琇娟 Hsu, Hsiu-Chuan |
| 學位類別： |
碩士
Master |
| 系所名稱： |
理學院 - 應用物理研究所 Graduate Institute of Applied Physics |
| 論文出版年： | 2025 |
| 畢業學年度： | 113 |
| 語文別： | 英文 |
| 論文頁數： | 60 |
| 中文關鍵詞： | 超導量子位元 、讀取保真度 、熱屏蔽塗層 、紅外光吸收塗層 、有效量子位元溫度 |
| 外文關鍵詞： | Superconducting qubit, Readout fidelity, Thermal shield coating, IR-absorbing coating, Effective qubit temperature |
| 相關次數： | 點閱：27 下載：0 |
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在發展量子計算技術的過程中，提升讀取保真度（readoutfidelity）是關鍵目標之一。然而，環境中的紅外輻射會引發不必要的態躍遷，從而降低保真度。這類錯誤可分為兩種機率事件，分別為當量子位元被準備於基態卻被測得為激發態的機率P(1|0)，以及準備於激發態卻被測得為基態的機率P(0|1)。
在本論文中，我們在低溫系統之底部裝載（bottom-loading）的屏蔽內側塗上具吸收紅外能力的黑色塗層，比較其對量子位元讀出表現的影響。為進一步理解其背後物理機制，我們亦量測了有效量子位元溫度與相干時間（coherencetimes）隨環境溫度的變化。
我們的研究結果顯示，有黑色塗層的情況下P(1|0)與P(0|1)較低，使讀出保真度由89%提升至93%，證實這種方式確實簡單且有效地降低紅外輻射對單一量子位元的影響，改善我們量測系統的低溫環境。
Achieving high readout fidelity is one of the primary goals in the pursuit of practical quantum computing. However, environmental infrared radiation degrades this fidelity by causing unwanted state transitions. One source of the errors is quantified by P(1|0), the probability of measuring an excited state when a qubit is prepared in the ground state, and P(0|1), the probability of measuring a ground state when prepared in an excited state.
In this thesis, we coated the inner surface of the shielding in a cryogenic bottom-loading system with an IR-absorbing black coating and compared its effect on the qubit readout performance. To further understand the underlying physics, we also studied the temperature dependence of the effective qubit temperature and coherence times.
Our results show that with the black coating, P(1|0) and P(0|1) were lower, leading to an improved readout fidelity from 89% to 93%. This verifies that this method is indeed a simple and effective way to reduce the effect of infrared radiation on a single qubit, improving the cryogenic environment of our measurement system.
Acknowledgement i
摘要 ii
Abstract iii
Contents iv
List of Figures vii
List of Tables viii
Chapter 1 Introduction 1
Chapter 2 Theory of Superconducting Qubits 3
2.1 Quantum Harmonic Oscillator 4
2.2 Transmon Qubit 6
2.3 Qubit-resonator Interaction 8
2.4 Decoherence 10
2.4.1 Energy-relaxation Time 𝑇1 11
2.4.2 Dephasing Time 𝑇 ∗ 12
2.5 Qubit Effective Temperature 13
Chapter 3 Qubit Design and Simulation 15
3.1 Transmission Line and Readout Resonator 16
3.2 Qubit 19
3.3 Coupling Strength Between Qubit and Resonator 21
3.4 Purcell Decay Rate 22
3.5 Summary 23
Chapter 4 Experimental Methods 25
4.1 Experimental Setup 26
4.1.1 Qubit Chip Design and Fabrication 26
4.1.2 FSE and Cryogenic Wiring 28
4.1.3 Qubit Control and Readout Electronics 31
4.2 Single Qubit Properties 32
4.3 Single-shot Readout 33
4.3.1 Pulse Schedule, Raw data on the IQ Plane and the Analysis Method 33
4.3.2 Readout Fidelity 35
Chapter 5 Data Analysis 38
5.1 Coating Effect Comparison 39
5.2 Readout Improvement 41
5.2.1 Readout Frequency Calibration 41
5.2.2 Readout Duration 42
5.2.3 Readout Amplitude 44
5.3 Temperature Dependence 47
5.3.1 𝑇𝑒𝑓𝑓 and Probability of Prepared-ground Error 𝑃 (1|0) 47
5.3.2 Coherence Time 49
Chapter 6 Discussion and Future Look 52
6.1 Discussion 52
6.2 Future Work 53
Bibliography 54
Appendix A Eight Resonators 58
Appendix B Coating Effects Comparison of a Neighboring Qubit 60
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全文公開日期 2026/08/15