使用磁屏蔽罩以及紅外光吸收塗層改善量子超導電路之性能

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姓名

張文庭(Wen-Ting Chang) 查詢紙本館藏

畢業系所

物理學系

論文名稱

使用磁屏蔽罩以及紅外光吸收塗層改善量子超導電路之性能
(Improving Performance of Superconducting Quantum Circuits by Magnetic Shielding and Infrared Absorbing Coatin照)

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摘要(中)

超導量子位元電路的同調性能對於量子計算是至關重要的一環。足夠長的量子位元存活時間 T1 對量子處理器進行量子閘的操作過程是必須的。使用在量子計算中的超導量子電路的性能受到各種損耗而受限，我們的對策是找出這些損耗機制的來源並設計相應的遮罩來提升性能。這篇論文將呈現對於磁場遮蔽罩、紅外光吸收塗層以及密封遮罩之效果的研究。磁場遮蔽罩是一個由mu-metal金屬製成的圓筒形遮罩，mu-metal有非常高的磁導率使得它擁有很好的遮蔽效果，在0.1mT外部磁場的模擬中達到小於-50 dB的遮蔽性能。在我們的量測中，量子位元內部品質因子Qi、存活時間T1以及退相位時間T2是量子位元性能的指標。這些參數同樣受上述損耗機制的影響。量測皆在稀釋製冷機中進行，並且使用來自威斯康辛大學麥迪遜分校McDermott 教授提供的超導量子位元電路樣品。在沒有遮罩的量測中，T1 = 10.9 µs以及T2 = 2.89 µs，在所有遮罩都被安裝的量測中，性能提
升至T1 = 28.0 µs以及T2 = 5.30 µs。內部品質因子Qi、存活時間T1以及退相位時間T2的提升顯示遮罩在我們的架設下超導量子位元電路的同調性能的提升。

摘要(英)

The coherence performance of superconducting qubits is crucial for quantum computing. For a quantum processor, a sufficiently long coherence is essential for the quantum gate operation processes. The coherence performance of superconducting circuits for quantum computing is limited by losses. Finding out the sources of the loss mechanisms and designing shielding for them is our strategy to improve the
performance. In this thesis, we present a study of the shielding effects of mu-metal shielding, infrared absorbing coating, and sealing shield. The magnetic shielding is
a cylinder can made of mu-metal. The mu-metal has very high permeability which makes the shielding have good shielding performance under -50 dB in the 0.1mT external magnetic field simulations. In our measurement, qubit quality factor Qi, relaxation time T1, and dephasing time T2 are an indicators for qubit performance. These parameters are subject to the effect of the loss mechanisms mentioned above. Measurements were performed in a dilution refrigerator with a superconducting qubit sample from the Prof. McDermott group at the University of Wisconsin Madison. For the qubit without shielding, T1 = 10.9 µs and T2 = 2.89 µs with qubit frequency at 5.229 GHz. The qubit with all shielding has better T1 = 28.0 µs and T2 = 5.30 µs with qubit frequency at 5.145 GHz. The improved Qi
, T1 and T2 shows the successful shielding.

關鍵字(中)

★ 量子位元

關鍵字(英)

★ qubit

論文目次

Abstract i
Contents ii
List of Figures iv
1 Introduction 1
1.1 Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2 Theory 8
2.1 Qubit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.1.1 Bloch Sphere . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2 Superconducting Qubit . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.2.1 Quantum LC Circuit . . . . . . . . . . . . . . . . . . . . . . . 10
2.2.2 Josephson Junction . . . . . . . . . . . . . . . . . . . . . . . . 11
2.2.3 Transmon Qubit . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.3 Jaynes-Cummings Hamiltonian . . . . . . . . . . . . . . . . . . . . . 15
2.3.1 Decoherence . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.4 Sources of Loss for Superconducting Circuit . . . . . . . . . . . . . . 17
2.4.1 TLS loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.4.2 Quasiparticle Loss . . . . . . . . . . . . . . . . . . . . . . . . 17
2.4.3 Magnetic Trapped Vortex . . . . . . . . . . . . . . . . . . . . 18
2.5 Magnetic Shielding . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.5.1 Meissner effect . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.5.2 Mu-metal Shielding Effect . . . . . . . . . . . . . . . . . . . . 20
3 Design and Fabrication 22
3.1 Shielding Superconducting Circuits . . . . . . . . . . . . . . . . . . . 22
3.2 Mu-metal Shielding design . . . . . . . . . . . . . . . . . . . . . . . . 22
3.2.1 Simulations of Magnetic Shielding . . . . . . . . . . . . . . . . 24
3.3 Infrared Light Absorbing . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.3.1 IR Absorbing Coating . . . . . . . . . . . . . . . . . . . . . . 25
3.4 Sealing Shield . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.5 Thermal Anchoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
4 Experimental Setup 30
4.1 3He-4He Dilution Refrigeration . . . . . . . . . . . . . . . . . . . . . . 30
4.2 Shielding Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
4.3 Circuit Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
5 Experimental Results 35
5.1 T1 Relaxation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
5.2 T2 Ramsey Characterization . . . . . . . . . . . . . . . . . . . . . . . 36
5.3 Shielding Configuration and Results . . . . . . . . . . . . . . . . . . . 37
5.4 Temperature Improvement . . . . . . . . . . . . . . . . . . . . . . . . 39
6 Conclusion 41
Reference 42

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指導教授

陳永富(Yung-Fu Chen)

審核日期

2024-7-2

推文