量子测量及其反作用
发布时间：2019-06-03 12:13
【摘要】：经典物理学中的测量过程,不妨可以理解为对被测者客观物理实在的忠实且不加改变的提取。然而在量子体系中,“物理实在”的内涵变得值得商榷,而测量过程也一般也不可避免的对被测系统产生影响,此即量子测量对被测系统的反作用。表现为不确定性、非定域性、互文性等等的量子世界与经典经验之间的种种不同,既“鬼魅般的折磨着每一个科学家的灵魂”,又呈现出缤纷炫丽的新物理,也已初见端倪的指引着技术的发展。这其中,量子测量和控制是极为重要的基础。本论文将从量子弱测量和弱值,量子测量中的误差和干扰关系,以及一个具体的量子光-机械振子系统的基态制备(被动冷却),这三个角度来对量子测量及其反作用“管窥蠡测”。“弱测量”特指具有后选择过程的较弱的测量。不同于通常量子力学公设中的投影测量(强测量),弱测量得到的测量结果反映在“弱值”里,而非通常的“期望值”。依定义,弱值可以是复数,模值可以超过所测力学量的本征谱范围。这些性质令人匪夷所思,也得到了很多精巧的应用。由概念的命名可以看出,“弱”字强调了此中测量对系统的可以忽略不计的反作用。而本文将介绍一个出乎意料的结果：我们修饰了弱值的定义,将其中一个平庸的因子换成了一个在实验直接可得的量,并建立了一个新弱值的严格理论,发现“弱值”实际上可以用任意强度的测量(有后选择步骤)得到,即测量的反作用强弱与否无关紧要。这一结果可以有效解决弱值理论在一大类应用中的效率等问题。测量的反作用是对系统状态的扰动,直觉上,这种扰动的大小和量子测量的准确度之间存在互补关系。但这种互补关系直到最近才得到学界的关注,而且引起了不大不小的争论。作为本论文的第二个主题,我们将介绍相关背景,并提出一个全新的理论,它避免了之前理论中存在的一些问题,并揭示出这种测量误差-干扰关系同量子不确定性之间的联系。我们发现,在态相关的意义下,如果用概率结果的分布作为量化误差和扰动的依据,那么,这种误差-干扰的互补关系存在与否,是由相关力学量不确定度的大小来决定的。以上都是对量子基础理论的研究。在第三个部分,我们将关注一个具体的光-机械振子系统(或称光力系统)。此系统最初是利用光场来间接测量机械振子所受微小力学效应的,尤其是引力波探测的LIGO项目。随着技术发展,现在已经得到更多的发展,在量子信息操控、量子物理基础等方面的研究都有重要的意义。在这个系统中,可以利用光场测量机械振子的位移或者受力,也可以利用此反作用来给振子制造阻尼,从而自动降低机械振子的能量量子数,实现对振子的准基态冷却。标准的冷却方案在系统参数位于边带不可析区域时失效,我们开发了一个方案来解决这个问题。
[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.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O413
本文编号：2491930
[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.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O413
【参考文献】
相关期刊论文 前1条
1 刘永椿;胡毓文;黄智维;肖云峰;;Review of cavity optomechanical cooling[J];Chinese Physics B;2013年11期
，本文编号：2491930
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