Are you an EPFL student looking for a semester project?
Work with us on data science and visualisation projects, and deploy your project as an app on top of GraphSearch.
Concept
Angular momentum operator
Summary
In quantum mechanics, the angular momentum operator is one of several related operators analogous to classical angular momentum. The angular momentum operator plays a central role in the theory of atomic and molecular physics and other quantum problems involving rotational symmetry. Such an operator is applied to a mathematical representation of the physical state of a system and yields an angular momentum value if the state has a definite value for it. In both classical and quantum mechanical systems, angular momentum (together with linear momentum and energy) is one of the three fundamental properties of motion.
There are several angular momentum operators: total angular momentum (usually denoted J), orbital angular momentum (usually denoted L), and spin angular momentum (spin for short, usually denoted S). The term angular momentum operator can (confusingly) refer to either the total or the orbital angular momentum. Total angular momentum is always conserved, see Noether's theorem.
In quantum mechanics, angular momentum can refer to one of three different, but related things.
The classical definition of angular momentum is . The quantum-mechanical counterparts of these objects share the same relationship:
where r is the quantum position operator, p is the quantum momentum operator, × is cross product, and L is the orbital angular momentum operator. L (just like p and r) is a vector operator (a vector whose components are operators), i.e. where Lx, Ly, Lz are three different quantum-mechanical operators.
In the special case of a single particle with no electric charge and no spin, the orbital angular momentum operator can be written in the position basis as:
where ∇ is the vector differential operator, del.
Spin (physics)
There is another type of angular momentum, called spin angular momentum (more often shortened to spin), represented by the spin operator . Spin is often depicted as a particle literally spinning around an axis, but this is only a metaphor: the closest classical analog is based on wave circulation.
Official source
About this result
This page is automatically generated and may contain information that is not correct, complete, up-to-date, or relevant to your search query. The same applies to every other page on this website. Please make sure to verify the information with EPFL's official sources.
Related publications (2)
An on/off Berry phase switch in circular graphene resonators
Donat Fabian Natterer, Yue Zhao
The phase of a quantum state may not return to its original value after the system's parameters cycle around a closed path; instead, the wave function may acquire a measurable phase difference called
American Association for the Advancement of Science2017Angular Resolved low loss EELS for Materials Characterization
Electron Energy Loss Spectrometry (EELS) in Transmission Electron Microscopy (TEM) is a powerful tool for the investigation of the electronic structure of materials. In the low loss regime, one can ac
EPFL2013Related concepts (66)
Rotation operator (quantum mechanics)
This article concerns the rotation operator, as it appears in quantum mechanics. With every physical rotation , we postulate a quantum mechanical rotation operator which rotates quantum mechanical states. In terms of the generators of rotation, where is rotation axis, is angular momentum, and is the reduced Planck constant. Translation operator (quantum mechanics) The rotation operator , with the first argument indicating the rotation axis and the second the rotation angle, can operate through the translation operator for infinitesimal rotations as explained below.
Spin (physics)
Spin is an intrinsic form of angular momentum carried by elementary particles, and thus by composite particles such as hadrons, atomic nuclei, and atoms. Spin should not be understood as in the "rotating internal mass" sense: spin is a quantized wave property. The existence of electron spin angular momentum is inferred from experiments, such as the Stern–Gerlach experiment, in which silver atoms were observed to possess two possible discrete angular momenta despite having no orbital angular momentum.
Angular momentum operator
In quantum mechanics, the angular momentum operator is one of several related operators analogous to classical angular momentum. The angular momentum operator plays a central role in the theory of atomic and molecular physics and other quantum problems involving rotational symmetry. Such an operator is applied to a mathematical representation of the physical state of a system and yields an angular momentum value if the state has a definite value for it.
Related courses (41)
PHYS-101(en): General physics : mechanics (English)
Students will learn the principles of mechanics to enable a better understanding of physical phenomena, such as the kinematics and dyamics of point masses and solid bodies. Students will acquire the c
PHYS-101(g): General physics : mechanics
Le but du cours de physique générale est de donner à l'étudiant les notions de base nécessaires à la compréhension des phénomènes physiques. L'objectif est atteint lorsque l'étudiant est capable de pr
PHYS-100: Advanced physics I (mechanics)
La Physique Générale I (avancée) couvre la mécanique du point et du solide indéformable. Apprendre la mécanique, c'est apprendre à mettre sous forme mathématique un phénomène physique, en modélisant l
Related MOOCs (14)
Newton's Mechanics
Ce cours de Physique générale – mécanique fourni les outils permettant de maîtriser la mécanique newtonienne du point matériel.
Point System Mechanics
Ce cours de Physique générale – mécanique fourni les outils permettant de maîtriser la mécanique newtonienne du point matériel.
Rigid Body Mechanics
Ce cours de Physique générale – mécanique fourni les outils permettant de maîtriser la mécanique newtonienne du point matériel.