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Symmetry and topology 对称与拓扑学
Pub Date : 2019-09-10 DOI: 10.1093/oso/9780198808350.003.0013
I. Kenyon
Space-time symmetries, conservation laws and Nöther’s theorem are discussed. The Poincaré group, generators and Casimir invariants are outlined. Local charge conservation and the corresponding U(1) charge symmetry underlying electromagnetism are presented, showing the roles of minimal electromagnetic coupling and gauge transformations. Experimental demonstrations of the Aharonov–Bohm effect are described and the topological interpretation is recounted. How the Aharonov–Casher effect survives in the classical world is mentioned. Berry’s revelation of geometric phase is presented. The Bitter–Dubbers experiment confirming this analysis is presented. Some comments are given on a Hilbert space with a simple topology.
讨论了时空对称性、守恒定律和Nöther定理。概述了庞加莱群、产生子和卡西米尔不变量。给出了电磁学中的局部电荷守恒和相应的U(1)电荷对称,说明了最小电磁耦合和规范变换的作用。描述了Aharonov-Bohm效应的实验证明,并叙述了拓扑解释。文中提到了阿哈罗诺夫-卡舍尔效应在古典世界中是如何存在的。介绍了贝瑞对几何相位的启示。Bitter-Dubbers实验证实了这一分析。给出了具有简单拓扑的希尔伯特空间的一些注释。
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引用次数: 2
EPR and Bell’s theorem, and quantum algorithms EPR和贝尔定理,还有量子算法
Pub Date : 2019-09-10 DOI: 10.1093/oso/9780198808350.003.0010
I. Kenyon
EPR showed that quantum mechanics is not a local deterministic theory and on this account they argued that it is incomplete. Quantum mechanics predicts correlations over time-like separations. The suggested resolution in terms of local hidden variables is presented. Bell’s analysis leading to experimental tests is described. The experiment of Aspect, Grangier and Roger vindicating quantum mechanics is described. More refined experiments, avoiding conceivable biases, confirm this result. Then computing based on quantum principles is discussed. Bits with two states in a register would be replaced by qubits with values represented by points on the Bloch sphere. Basic gates are presented. Shor’s algorithm to decompose products of primes is described and a gate structure presented to implement it. Implementation would undermine current encryption methods. Quantum cryptography is described using the BB84 protocol. The no-cloning theorem protects this absolutely against attempts to intercept the encryption data.
EPR表明,量子力学不是一个局部确定性理论,因此他们认为它是不完整的。量子力学预测了类时间分离的相关性。给出了基于局部隐变量的解决方法。描述了贝尔的分析导致实验测试。描述了Aspect、Grangier和Roger对量子力学的验证实验。更精细的实验,避免了可能的偏差,证实了这一结果。然后讨论了基于量子原理的计算。寄存器中具有两种状态的比特将被量子位取代,量子位的值由布洛赫球上的点表示。给出了基本门。描述了分解素数乘积的肖尔算法,并给出了实现该算法的门结构。实现将破坏当前的加密方法。量子密码学使用BB84协议进行描述。不可克隆定理绝对防止试图拦截加密数据。
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引用次数: 0
Entanglement 纠缠
Pub Date : 2019-09-10 DOI: 10.1093/oso/9780198808350.003.0009
I. R. Kenyon
The distiction between classical product states and quantum entangled states is disclosed with examples. Spontaneous parametric down conversion as a source of entangled photons is described. The action of a perfect beam splitter is analysed using creation and annihilation operators. The HOM interferometer is described. Its use in demonstrating the indistinguishability of photons and in measuring bandwidth of sources at the level of femtoseconds is recounted. Two particle entanglement is analysed using the Bloch sphere representation showing how the full knowledge of the entangled state does not fix the state of the individual particles. The four Bell states, eigenstates of two particle entanglement, are introduced. Teleportation of a photon state using entangled photons is described, and an experiment to entangle the quantum states of atoms at space-like separation outlined.
通过实例揭示了经典积态与量子纠缠态的区别。描述了作为纠缠光子源的自发参量下转换。用产生和湮灭算符分析了理想分束器的作用。描述了HOM干涉仪。叙述了它在证明光子不可分辨性和测量飞秒级光源带宽方面的应用。使用布洛赫球表示分析了两个粒子的纠缠,显示了纠缠态的全部知识如何不能固定单个粒子的状态。介绍了双粒子纠缠的四种贝尔态,即本征态。描述了利用纠缠光子的隐形传态,并概述了在类空间分离时纠缠原子量子态的实验。
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引用次数: 0
Quantum Hall effects 量子霍尔效应
Pub Date : 2019-09-10 DOI: 10.1093/oso/9780198808350.003.0017
I. Kenyon
It is explained how plateaux are seen in the Hall conductance of two dimensional electron gases, at cryogenic temperatures, when the magnetic field is scanned from zero to ~10T. On a Hall plateau σ‎xy = ne 2/h, where n is integral, while the longitudinal conductance vanishes. This is the integral quantum Hall effect. Free electrons in such devices are shown to occupy quantized Landau levels, analogous to classical cyclotron orbits. The stability of the IQHE is shown to be associated with a mobility gap rather than an energy gap. The analysis showing the topological origin of the IQHE is reproduced. Next the fractional QHE is described: Laughlin’s explanation in terms of an IQHE of quasiparticles is presented. In the absence of any magnetic field, the quantum spin Hall effect is observed, and described here. Time reversal invariance and Kramer pairs are seen to be underlying requirements. It’s topological origin is outlined.
解释了在低温下,当磁场从0到~10T扫描时,二维电子气体的霍尔电导是如何出现平台的。在霍尔平台上σ _ (xy) = ne 2/h,其中n为积分,而纵向电导消失。这就是积分量子霍尔效应。这种装置中的自由电子被证明占据量子化朗道能级,类似于经典回旋加速器轨道。IQHE的稳定性被证明与迁移率间隙而不是能量间隙有关。分析显示的拓扑起源的IQHE是复制。接下来描述分数QHE:劳克林在准粒子的IQHE方面的解释被提出。在没有任何磁场的情况下,量子自旋霍尔效应被观察到,并在这里描述。时间反转不变性和克莱默对被认为是潜在的要求。概述了它的拓扑起源。
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引用次数: 0
Superfluid 4He 超流体他
Pub Date : 2019-09-10 DOI: 10.1093/oso/9780198808350.003.0014
I. Kenyon
The superfluid transition of 4He at 2.17K to He-II and the inference of an underlying condensate are introduced. The fountain effect is interpreted. Andronikashvili’s experiment and the determination of superfluid fraction versus temperature are discussed. Sound and second sound are described. Relationships between the condensate and superfluid fractions, and to off diagonal long-range order (ODLRO) are deduced. The revelation of topological quantization of circulation by Vinen’s experiment is recounted. Spontaneous symmetry breaking by the condensate’s phase coherence is explained. Excitations and their dispersion relations described with Landau’s interpretation, including the explanation of the critical velocity of superflow. Vortices, their interpretation in terms of quantized circulation, and their visualization are described.
介绍了在2.17K时4He向He-II的超流体跃迁和下伏凝析物的推断。喷泉效应得到了解释。讨论了Andronikashvili的实验和超流体分数随温度的测定。描述一个音和第二个音。推导了凝析液与超流体馏分之间的关系,以及离对角线长程序的关系。叙述了维宁实验对循环拓扑量子化的启示。解释了凝聚体相相干的自发对称性破缺。用朗道的解释描述了激发态及其色散关系,包括超流临界速度的解释。描述了涡旋、它们在量子化环流方面的解释以及它们的可视化。
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引用次数: 0
Phonons 声子
Pub Date : 2019-09-10 DOI: 10.1093/oso/9780198808350.003.0004
I. Kenyon
Phonons are introduced as an example of quasi-particles that can only exist in matter. Debye’s quantum model for heat capacity of solids and comparison with experimentin different temperature ranges is presented. The dispersion relations of lattice vibration (phonons) and quantization for chains of atoms presented, revealing the optical and acoustic modes; anharmonic effects are discussed. Crystal lattice structures and Brillouin zones are introduced. Phonon scattering and the Umklapp process described. The variation of the thermal conductivity of dielectrics with temperature is interpreted. X-ray scattering studies of phonon dispersion relations are described. Coupling between phonons with photons in polaritons is explained: Raman scattering studies of GaN used to exhibit the cross-over of their dispersion relations. The Mössbauer effect, a recoilless process, and its dependence on temperature are explained.
声子是一类只能存在于物质中的准粒子。给出了固体热容的德拜量子模型,并与实验结果进行了比较。给出了原子链晶格振动(声子)与量子化的色散关系,揭示了原子链的光学和声学模式;讨论了非调和效应。介绍了晶体点阵结构和布里渊带。声子散射和Umklapp过程描述。解释了电介质导热系数随温度的变化规律。描述了声子色散关系的x射线散射研究。解释了声子与光子在极化子中的耦合:氮化镓的拉曼散射研究显示了它们色散关系的交叉。解释了Mössbauer效应、无后坐力过程及其对温度的依赖关系。
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引用次数: 0
Field quantization 场量子化
Pub Date : 2019-09-10 DOI: 10.1093/oso/9780198808350.003.0008
I. Kenyon
Field or second quantization is carried through for electromagnetism, giving creation and annihilation operators for photons. Vacuum energy arises from field fluctuations, which causes the Casimir force and the Lamb shift of spectral lines. The connection between absorption, spontaneous emission and the stimulated emission of radiation is shown to emerge naturally. This yields Einstein’s equations for radiation in thermal equilibrium. The prerequisites for lasing, the operation and the properties of lasers are described. Fully coherent (Laser) states are expressed in terms of Fock states. The first and second order coherence of lasers and thermal sources are worked out. The Hanbury Brown and Twiss experiment is described and the application of the principle to determining stellar sizes and interaction regions in particle collisions from meson correlations are described.
电磁场的场量子化或二次量子化,为光子提供创造和湮灭算子。真空能量来源于场涨落,引起了卡西米尔力和谱线的兰姆位移。辐射的吸收、自发发射和受激发射之间的联系是自然出现的。这就产生了爱因斯坦的热平衡辐射方程。介绍了激光的前提条件、激光器的操作和特性。全相干(激光)态用Fock态表示。计算了激光和热源的一阶和二阶相干性。描述了Hanbury Brown和Twiss实验,并描述了从介子相关中确定粒子碰撞中恒星大小和相互作用区域的原理的应用。
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引用次数: 157
Particle physics II 粒子物理II
Pub Date : 2019-09-10 DOI: 10.1093/oso/9780198808350.003.0019
I. Kenyon
Quantum chromodynamics the quantum gauge theory of strong interactions is presented: SU(3) being the (colour) symmetry group. The colour content of strongly interacting particles is described. Gluons, the field particles, carry colour so that they mutually interact – unlike photons. Renormalization leads to the coupling strength declining at large four momentum transfer squared q 2 and to binding of quarks in hadrons at small q 2. The cutoff in the range of the strong interaction is shown to be due to this low q 2 behaviour, despite the gluon being massless. In high energy interactions, say proton-proton collisions, the initial process is a hard (high q 2) parton+parton to parton+parton process. After which the partons undergo softer interactions leading finally to emergent hardrons. Experiments at DESY probing proton structure with electrons are described. An account of electroweak unification completes the book. The weak interaction symmetry group is SUL(2), L specifying handedness. This makes the electroweak symmetry U(1)⊗SUL(2). The weak force carriers, W± and Z0, are massive, which is at odds with the massless carriers required by quantum gauge theories. How the BEH mechanism resolves this problem is described. It involves spontaneous symmetry breaking of the vacuum with scalar fields. The outcome are massive gauge field particles to match the W± and Z0 trio, a massless photon, and a scalar field with a massive particle, the Higgs boson. The experimental programmes that discovered the vector bosons in 1983 and the Higgs in 2012 are described, including features of generic detectors. Finally puzzles revealed by our current understanding are outlined.
提出了量子色动力学中强相互作用的量子规范理论:SU(3)为(色)对称群。描述了强相互作用粒子的颜色含量。胶子,场粒子,携带颜色,所以它们相互作用——不像光子。重正化导致耦合强度在大的动量传递平方q 2处下降,在小的q 2处导致夸克在强子中的结合。尽管胶子是无质量的,但在强相互作用范围内的截止是由于这种低q 2行为。在高能相互作用中,比如质子-质子碰撞,初始过程是一个艰难的(高q2) parton+parton到parton+parton过程。在此之后,粒子经历较软的相互作用,最终导致出现强子。描述了在DESY上用电子探测质子结构的实验。关于电弱统一的叙述完成了这本书。弱相互作用对称群为SUL(2), L表示手性。这使得电弱对称性为U(1)⊗SUL(2)。弱力载流子W±和Z0是有质量的,这与量子规范理论要求的无质量载流子不一致。描述了BEH机制如何解决这个问题。它涉及到真空与标量场的自发对称性破缺。其结果是与W±和Z0三重奏相匹配的大质量规范场粒子,一个无质量光子,以及一个具有大质量粒子希格斯玻色子的标量场。描述了1983年发现矢量玻色子和2012年发现希格斯玻色子的实验项目,包括通用探测器的特点。最后概述了我们目前的认识所揭示的困惑。
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引用次数: 0
Transitions 转换
Pub Date : 2019-09-10 DOI: 10.1093/oso/9780198808350.003.0007
I. Kenyon
A derivation of Fermi’s golden rule is given: this is the interface into which matrix elements from theory can be slotted to provide a prediction testable by experiment. The example of the prediction of the 2p→1s decay in hydrogen is worked through in detail. Selection rules, spectral line shapes (Breit–Wigner and Gaussian) and broadening processes are explained. The formula for the experimental cross-section in terms of the matrix element is produced. The Born approximation is presented and applied to Rutherford scattering. Then the decay rate for allowed β‎-decays is calculated in Fermi’s model and fitted to the observed rates. Low energy s-wave scattering is analysed in terms of phase shift and scattering length. The example of cold alkali metal atom scattering (≤10−6eV) is treated in preparation for use later with gaseous Bose–Einstein condensates. Ramsauer–Townsend effect explained.
给出了费米黄金法则的一个推导:这是一个接口,从理论中可以插入矩阵元素,以提供可通过实验验证的预测。以氢的2p→1s衰变预测为例进行了详细的研究。解释了选择规则、谱线形状(Breit-Wigner和Gaussian)和展宽过程。给出了用矩阵元表示的实验截面计算公式。提出了玻恩近似,并将其应用于卢瑟福散射。然后在费米模型中计算允许β -衰变的衰变速率,并与观测到的速率拟合。从相移和散射长度两个方面分析了低能s波散射。以碱金属原子(≤10−6eV)的冷散射为例,为以后用气态玻色-爱因斯坦凝聚体作准备。Ramsauer-Townsend效应解释。
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引用次数: 0
Quantum statistics 量子统计
Pub Date : 2019-09-10 DOI: 10.1093/oso/9780198808350.003.0003
I. Kenyon
Indistinguishability of like particles, and the fermion and boson exchange symmetries discussed.Pauli exclusion principle and features of multi-electron atoms, including selection rules are discussed. Degeneracy pressure and the formation of compact stellar objects is analysed. Quantum exchange force between electrons and its contribution to ferromagnetism is outlined. Fermi-Dirac and Bose-Einstein statistics, includng the chemical potential are derived. The conditions for Bose-Einstein condensation are deduced; condensates and their stability are considered.
类粒子的不可区分性,以及费米子和玻色子交换对称性的讨论。讨论了泡利不相容原理和多电子原子的特性,包括选择规则。分析了简并压力与致密天体形成的关系。概述了电子间的量子交换力及其对铁磁性的贡献。推导了费米-狄拉克统计和玻色-爱因斯坦统计,包括化学势。推导了玻色-爱因斯坦凝聚的条件;考虑了凝析油及其稳定性。
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引用次数: 0
期刊
Quantum 20/20
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