【摘要】：超導(dǎo)量子比特作為人工原子,不但是實(shí)現(xiàn)量子計(jì)算的熱門方案,而且是研究量子力學(xué)本質(zhì)問題的有力工具。近年來在腔量子電動(dòng)力學(xué)系統(tǒng)基礎(chǔ)上發(fā)展起來的電路量子電動(dòng)力學(xué)系統(tǒng),是一種全新的量子比特。由于在退相干時(shí)間等參數(shù)上遠(yuǎn)遠(yuǎn)超出之前的超導(dǎo)量子比特,它受到了極大的關(guān)注。和”傳統(tǒng)”的超導(dǎo)量子比特不同,電路量子電動(dòng)力學(xué)系統(tǒng)使用微波諧振腔作為系統(tǒng)的讀出機(jī)構(gòu)。這樣的讀出機(jī)構(gòu)一方面可以減小超導(dǎo)量子比特和環(huán)境的耦合,提高退相干時(shí)間；另一方面給我們提供了全新的量子比特信息讀取方案一一量子非破壞性測量。此外,該結(jié)構(gòu)在系統(tǒng)集成等方面也具有顯著的優(yōu)勢。所以在目前的超導(dǎo)量子比特中,該系統(tǒng)的性能是最優(yōu)異的。本文首先介紹了量子計(jì)算,量子測量的基本概念以及三種“傳統(tǒng)”的量子比特：電荷比特,磁通比特和相位比特。然后系統(tǒng)的介紹電路量子電動(dòng)力學(xué)系統(tǒng)。該系統(tǒng)主要包括了諧振腔,人工原子,以及它們之間的耦合三大部分。本文中,作為人工原子的量子比特總共有三個(gè),分別是三維Transmon,二維Transmon和三維磁通比特；使用的諧振腔有兩種,一種是矩形波導(dǎo)諧振腔,由鋁或者無氧銅材料制作而成,另一種是共面波導(dǎo)諧振腔。當(dāng)把人工原子放置在諧振腔中使它們耦合在一起時(shí),就構(gòu)成了電路量子電動(dòng)力學(xué)系統(tǒng)。接著,論文著重介紹了在稀釋制冷機(jī)平臺(tái)上搭建的測量系統(tǒng),并介紹了兩種測量方法：亮態(tài)測量和量子非破壞性測量。在本文的最后,論文介紹了利用該測量系統(tǒng)測量電路量子電動(dòng)力學(xué)系統(tǒng)的結(jié)果。根據(jù)使用的能級(jí)數(shù)目不同分為二能級(jí)系統(tǒng)和三能級(jí)系統(tǒng)兩章。在二能級(jí)系統(tǒng)中,主要介紹了拉比振蕩,拉姆齊干涉,自旋回波,量子層析等。通過這些測量結(jié)果,獲取了二能級(jí)系統(tǒng)的退相干參數(shù)。在三能級(jí)系統(tǒng)中,主要介紹了暗態(tài),相干粒子數(shù)囚禁,奧特勒-湯尼斯劈裂和電磁感應(yīng)的透明等實(shí)驗(yàn)結(jié)果。在暗態(tài)和相干粒子數(shù)囚禁實(shí)驗(yàn)中,我們?cè)趯?shí)驗(yàn)上通過兩束微波成功的把三能級(jí)系統(tǒng)的態(tài)凍結(jié),使其不再隨時(shí)間演化。控制兩束微波的強(qiáng)度和相位,我們可以凍結(jié)任意的態(tài),所以該方法可以作為量子存儲(chǔ)的方案,在量子計(jì)算中有著重要作用。在奧特勒-湯尼斯劈裂實(shí)驗(yàn)中,我們測量了共振情況下的能級(jí)劈裂,該能級(jí)劈裂的大小和理論模擬完全吻合。為了觀察三能級(jí)的電磁感應(yīng)的透明,我們嘗試在三能級(jí)中引入噪聲,使得三能級(jí)系統(tǒng)滿足電磁感應(yīng)的透明的條件。雖然最后沒能看到預(yù)期的效果,但是根據(jù)能量弛豫時(shí)間的估算,該系統(tǒng)已經(jīng)進(jìn)入電磁感應(yīng)的透明的臨界條件。
[Abstract]:As an artificial atom, superconducting quantum bit is not only a popular scheme to realize quantum computation, but also a powerful tool to study the essential problems of quantum mechanics. In recent years, the circuit quantum electrodynamics system developed on the basis of cavity quantum electrodynamics system is a new kind of quantum bit. It has attracted much attention because it is far beyond the previous superconducting quantum bits in terms of decoherence time and other parameters. Unlike the "traditional" superconducting quantum bits, the circuit quantum electrodynamics system uses a microwave resonator as the readout mechanism of the system. On the one hand, the readout mechanism can reduce the coupling between the superconducting quantum bit and the environment and improve the decoherence time; on the other hand, it provides us with a new quantum bit information reading scheme, quantum nondestructive measurement. In addition, the structure also has significant advantages in system integration. Therefore, the performance of the system is the best among the current superconducting quantum bits. This paper first introduces the basic concepts of quantum computation, quantum measurement and three kinds of "traditional" quantum bits: charge bit, magnetic flux bit and phase bit. Then the circuit quantum electrodynamics system is introduced systematically. The system consists of three parts: resonator, artificial atom and coupling between them. In this paper, there are three quantum bits as artificial atoms, which are three-dimensional Transmon, two-dimensional Transmon and three-dimensional flux bits. There are two kinds of resonators used, one is rectangular waveguide resonator, which is made of aluminum or oxygen free copper. The other is coplanar waveguide resonator. When artificial atoms are placed in the resonator to couple them together, a circuit quantum electrodynamics system is constructed. Then, the paper mainly introduces the measurement system built on the platform of dilution refrigerator, and introduces two measuring methods: bright state measurement and quantum nondestructive measurement. At the end of this paper, the results of quantum electrodynamics system are introduced. According to the number of energy levels used, it can be divided into two chapters: the two-level system and the three-level system. In the two-level system, the Rabi oscillation, Ramsay interference, spin echo, quantum chromatography and so on are introduced. Through these measurements, the decoherence parameters of the two-level system are obtained. In the three-level system, the experimental results of dark state, coherent particle number trapping, Otell-Tonys splitting and the transparency of electromagnetic induction are introduced. In the experiments of dark state and coherent particle number trapping, we have successfully frozen the state of the three-level system by two microwave beams, so that it no longer evolves with time. We can freeze arbitrary states by controlling the intensity and phase of two microwave beams, so this method can be used as a quantum storage scheme and plays an important role in quantum computation. In the Otleer-Tonys splitting experiment, we measured the energy level splitting in the resonance case, and the size of the energy level splitting is in good agreement with the theoretical simulation. In order to observe the transparency of the three-level electromagnetic induction, we try to introduce noise into the three-level system so that the three-level system satisfies the condition of the transparency of the electromagnetic induction. Although the desired effect was not observed in the end the system has entered the critical condition of electromagnetically induced transparency according to the estimation of the energy relaxation time.
【學(xué)位授予單位】：南京大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：O413.2

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