放大是測量微弱電訊號必要的步驟。雖然放大器可以提供所需的增益，但也 會在放大訊號時加入額外的雜訊，降低訊號與雜訊的比值（ SNR）。約瑟夫 森參量放大器（ JPA）包含由約瑟夫森接面製成的諧振器，使得訊號得以被 放大。它不僅可以在微波頻率上提供高增益，還具有接近量子極限外加噪聲 的特性。這個元件被廣泛地運用在各種量子量測上面，比方說，量子位元的 量測、軸子的偵測。近期各種的實驗都需要寬頻的放大器，因此我將介紹一 個由四分之一波長和半波長波導管所組成的寬頻約瑟夫森放大器。這篇論文 主要是參考 Appl. Phys. Lett. 107, 262601 (2015) 的理論和設計。在實驗裡， IMPA 的調頻範圍非常窄～150 MHz，增益值大約 2.5 dB。表現這麼差的原 因我們覺得是 Josephson junctions 的不對稱所造成的。為了解決這個問題， 我們正在尋找製程上最佳的參數。;Amplification is necessary for measuring small-amplitude electrical signals. Although the amplifier can provide the required amplification, it also adds extra noise to the amplified signal and reduces the signal-to-noise ratio (SNR). A Josephson Parametric Amplifier (JPA) includes a resonator made of Josephson junctions allowing parametric modulation. It can provide high gain in microwave frequencies and have near quantum-limited noise performance to boost measurement SNR. Recent demands in measuring microwave signals from superconducting circuits for quantum information have driven the intensive development of JPAs. The rapid progress towards scalable quantum processors demands amplifiers with large bandwidths. For this purpose, I present a broadband JPA integrated with an on-chip impedance transformer including a quarter-wave and half-wave coplanar waveguide. The theory and design ideas are from Appl. Phys. Lett. 107, 262601 (2015). The tuning range of the IMPA resonator in this thesis is very narrow (150 MHz) and the gain is 2.5 dB. We think the main problem is from the asymmetry of Josephson junctions. To solve this problem, we are making efforts to control the fabrication parameters and find the optimal value to fabricate JPA.
