【摘要】：經典物理學中的測量過程,不妨可以理解為對被測者客觀物理實在的忠實且不加改變的提取。然而在量子體系中,“物理實在”的內涵變得值得商榷,而測量過程也一般也不可避免的對被測系統(tǒng)產生影響,此即量子測量對被測系統(tǒng)的反作用。表現(xiàn)為不確定性、非定域性、互文性等等的量子世界與經典經驗之間的種種不同,既“鬼魅般的折磨著每一個科學家的靈魂”,又呈現(xiàn)出繽紛炫麗的新物理,也已初見端倪的指引著技術的發(fā)展。這其中,量子測量和控制是極為重要的基礎。本論文將從量子弱測量和弱值,量子測量中的誤差和干擾關系,以及一個具體的量子光-機械振子系統(tǒng)的基態(tài)制備(被動冷卻),這三個角度來對量子測量及其反作用“管窺蠡測”�！叭鯗y量”特指具有后選擇過程的較弱的測量。不同于通常量子力學公設中的投影測量(強測量),弱測量得到的測量結果反映在“弱值”里,而非通常的“期望值”。依定義,弱值可以是復數(shù),模值可以超過所測力學量的本征譜范圍。這些性質令人匪夷所思,也得到了很多精巧的應用。由概念的命名可以看出,“弱”字強調了此中測量對系統(tǒng)的可以忽略不計的反作用。而本文將介紹一個出乎意料的結果：我們修飾了弱值的定義,將其中一個平庸的因子換成了一個在實驗直接可得的量,并建立了一個新弱值的嚴格理論,發(fā)現(xiàn)“弱值”實際上可以用任意強度的測量(有后選擇步驟)得到,即測量的反作用強弱與否無關緊要。這一結果可以有效解決弱值理論在一大類應用中的效率等問題。測量的反作用是對系統(tǒng)狀態(tài)的擾動,直覺上,這種擾動的大小和量子測量的準確度之間存在互補關系。但這種互補關系直到最近才得到學界的關注,而且引起了不大不小的爭論。作為本論文的第二個主題,我們將介紹相關背景,并提出一個全新的理論,它避免了之前理論中存在的一些問題,并揭示出這種測量誤差-干擾關系同量子不確定性之間的聯(lián)系。我們發(fā)現(xiàn),在態(tài)相關的意義下,如果用概率結果的分布作為量化誤差和擾動的依據(jù),那么,這種誤差-干擾的互補關系存在與否,是由相關力學量不確定度的大小來決定的。以上都是對量子基礎理論的研究。在第三個部分,我們將關注一個具體的光-機械振子系統(tǒng)(或稱光力系統(tǒng))。此系統(tǒng)最初是利用光場來間接測量機械振子所受微小力學效應的,尤其是引力波探測的LIGO項目。隨著技術發(fā)展,現(xiàn)在已經得到更多的發(fā)展,在量子信息操控、量子物理基礎等方面的研究都有重要的意義。在這個系統(tǒng)中,可以利用光場測量機械振子的位移或者受力,也可以利用此反作用來給振子制造阻尼,從而自動降低機械振子的能量量子數(shù),實現(xiàn)對振子的準基態(tài)冷卻。標準的冷卻方案在系統(tǒng)參數(shù)位于邊帶不可析區(qū)域時失效,我們開發(fā)了一個方案來解決這個問題。
[Abstract]:The measurement process in classical physics may be understood as the faithful and unchanging extraction of the objective physical reality of the subject. However, in quantum systems, the connotation of "physical reality" becomes open to question, and the measurement process is generally inevitable to have an impact on the system under test, that is, the reaction of quantum measurement to the system under test. The quantum world of uncertainty, non-localization, intertextuality and so on is different from the classical experience, which not only "haunts the soul of every scientist", but also presents colorful and dazzling new physics. It has also begun to guide the development of technology. Among them, quantum measurement and control is a very important basis. In this paper, the ground state preparation (passive cooling) of a specific quantum optical-mechanical oscillator system will be studied from the aspects of quantum weak measurement and weak value, the relationship between error and interference in quantum measurement, and the ground state preparation (passive cooling) of a specific quantum optical-mechanical oscillator system. From these three angles, we can see the quantum measurement and its reaction. "weak measurement" refers to a weaker measurement with a post-selection process. Different from the projection measurement (strong measurement) in the usual quantum mechanics postulate, the measurement results obtained by weak measurement are reflected in the "weak value" rather than the usual "expected value". By definition, the weak value can be complex and the modulus value can exceed the eigenspectrum range of the measured mechanical quantity. These properties are unthinkable and have been used in many exquisite ways. As can be seen from the naming of the concept, the word "weak" emphasizes the negligible reaction of measurement to the system. In this paper, we will introduce an unexpected result: we modify the definition of weak value, replace one of the mediocre factors with a quantity that is directly available in the experiment, and establish a strict theory of new weak value. It is found that the "weak value" can actually be obtained by the measurement of arbitrary strength (with the post-selection step), that is, whether the reaction of the measurement is strong or not does not matter. This result can effectively solve the problem of the efficiency of weak value theory in a large class of applications. The reaction of measurement is the disturbance to the state of the system. Intuitively, there is a complementary relationship between the magnitude of the disturbance and the accuracy of quantum measurement. However, this complementary relationship has only recently attracted the attention of the academic community, and has aroused considerable debate. As the second topic of this paper, we will introduce the relevant background and put forward a new theory, which avoids some problems existing in the previous theory. The relationship between the measurement error-interference relationship and quantum uncertainty is also revealed. We find that if the distribution of probability results is used as the basis of quantitative error and disturbance in the sense of state correlation, the existence of the complementary relationship between error and interference is determined by the uncertainty of related mechanical quantities. The above is the study of quantum basic theory. In the third part, we will focus on a specific optical-mechanical oscillator system (or optical force system). At first, the system uses light field to indirectly measure the micro-mechanical effects of mechanical oscillators, especially the LIGO project of gravitational wave detection. With the development of technology, more and more development has been made now, and the research on quantum information manipulation and quantum physical foundation is of great significance. In this system, the displacement or force of the mechanical oscillator can be measured by light field, and the damping can be made by using this reaction, so that the energy quantum number of the mechanical oscillator can be automatically reduced and the quasi-ground state cooling of the oscillator can be realized. The standard cooling scheme fails when the system parameters are in the non-analytical region of the sideband. We have developed a scheme to solve this problem.
【學位授予單位】：中國科學技術大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：O413

【參考文獻】

相關期刊論文 前1條

1 劉永椿;胡毓文;黃智維;肖云峰;;Review of cavity optomechanical cooling[J];Chinese Physics B;2013年11期

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本文編號：2491930