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| Title: | BCC鉭及單晶鋁〔111〕基共面波導共振腔的表現
The performance of coplanar waveguide resonators made of BCC tantalum and single crystal aluminium〔111〕 |
| Authors: | 黃正丞
Huang, Cheng-Cheng |
| Contributors: | 陳啟東
許琇娟
Chen, Chii-Dong
Hsu, Hsiu-Chuan
黃正丞
Huang, Cheng-Cheng |
| Keywords: | 超導
二能級系統
共面波導
Q factor
量子計算
Superconductor
Two level system
Coplanar waveguide
Q factor
Quantum computing |
| Date: | 2022 |
| Issue Date: | 2022-10-05 09:31:21 (UTC+8) |
| Abstract: | Transmon超導量子電腦晶片零件包含傳輸/讀取線（transmission/readout line）、共振腔（resonance cavity）、約瑟夫森接面（Josephson junction）、並聯電容板（parallel capacitor）及控制線（gate control）。在量子位元的操作上，弛豫時間（relaxation time, T1）是一項重要的參數，這項參數直接的指出了一個量子位元可以進行操作的最長時間，而這項時間長度會受到介電損失的「限制」，介電損失（dielectric loss）是在超導體的臨界溫度下，造成去相干（decoherence）的重要因子之一。
本文研究的介電損失形式為二能級系統（Two level system, TLS），二能級系統主要來源可分為三種：金屬-真空介面（metal-vacuum）、金屬-基板介面（metal-substrate），及基板-真空介面（substrate-vacuum），二能級系統會限制量子位元在弛豫時間的表現；製程及材料皆會對成品的二能級系統損失比例造成影響。本文探討了透過分析共面波導共振腔各種材料組合及製程方法來找出擁有最低的二能級系統損失，提高品質因子。
本實驗挑選技術成熟易加工的單晶鋁，及近期在文獻上弛豫時間上有著優秀的表現的BCC 鉭（α-Ta）進行共面波導共振腔製造，目的在於比較不同材料、製程及界面對共振腔成品表現的影響及各項製程的優缺點。材料部分，以濺鍍鋁長在矽基版上的樣品有著較高的品質因子，且能量相關性也相對穩定；介面部分，我們發現共平面共振腔間隙越寬，共振腔的本質品質因素越高，說明二氧化矽表面的二能級系統可能是主要的能量耗散機制。
The components of transmon superconducting quantum computer chip include transmission/readout line, resonance cavity, Josephson junction, parallel capacitor and gate control line. In the operation of qubits, an important parameter is the relaxation time (T1) of the qubits, which implies the maximum time that a qubit can be operated before it went decoherence, and the length of this time will be affected by the dielectric loss, which is the major factor of the decoherence.
The type of dielectric loss studied in this work is two-level system (TLS), which can located in the metal-vacuum interface, metal-substrate interface, and substrate-vacuum interface. The two-level system might present in the amorphous residuals results from the device manufacturing process.
We studied superconducting coplanar waveguide resonators made of crystalline Al and α-phase Ta combinations and fabrication process methods of coplanar waveguide resonators to figure out the combination with the lowest TLS loss, thereby improving the resonator quality factor.
In this thesis work, we studied single crystal aluminum and BCC tantalum (α-Ta) coplanar waveguide resonators made by e-beam lithography and dry-etching techniques. α-Ta resonators have been reported with an excellent performance on relaxation time recently, and was selected to examine the influence materials and fabrication processes and interfaces. We found that when the cavity photon number is small and the TLS dominates the loss mechanism, the sputtered Al on Si substrate has the highest internal quality factor. Furthermore, we noted that the larger the coplanar waveguide gap width, the higher the internal quality factor, suggesting that the loss is largely contributed by the substrate surface loss. |
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| Description: | 碩士
國立政治大學
應用物理研究所
109755005 |
| Source URI: | http://thesis.lib.nccu.edu.tw/record/#G0109755005 |
| Data Type: | thesis |
| DOI: | 10.6814/NCCU202201566 |
| Appears in Collections: | [應用物理研究所 ] 學位論文
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