In quantum physics, the concept of "spin" refers to an intrinsic property of elementary particles. Spin is not exactly the same as the classical notion of a spinning object; it's an intrinsic angular momentum that particles possess. To find a generalization for spin in quantum physics, we rely on experimental observations and theoretical models.
The initial understanding of spin came from experiments conducted by Otto Stern and Walther Gerlach in 1922, which involved passing a beam of silver atoms through an inhomogeneous magnetic field. They observed that the beam split into two distinct components, indicating that the silver atoms possessed an intrinsic angular momentum.
Later, in 1925, spin was incorporated into the mathematical framework of quantum mechanics by Wolfgang Pauli. He introduced the concept of spin as an additional quantum number that describes the behavior of particles beyond their position and momentum.
The generalization of spin in quantum physics can be summarized as follows:
Spin as an intrinsic property: Spin is a fundamental property of particles, just like mass or charge. It characterizes how a particle interacts with magnetic fields and affects its behavior.
Quantization of spin: Spin is quantized, meaning it can only take specific discrete values. For example, particles with half-integer spin are called fermions, such as electrons and quarks, while particles with integer spin are called bosons, such as photons.
Spin as angular momentum: Spin is often described in terms of angular momentum. However, unlike classical angular momentum, spin does not correspond to actual rotation in space. Instead, it is a purely quantum mechanical property that has no classical analogue.
Spin and superposition: Like other quantum properties, spin can exist in a superposition of different states. For example, an electron can be in a superposition of spin-up and spin-down states until it is measured or interacts with its environment.
Spin and spin operators: Spin is described mathematically using spin operators, which are analogous to position and momentum operators in quantum mechanics. These operators allow us to calculate the spin of particles and study their properties.
The generalization of spin in quantum physics has been extensively verified through numerous experiments and is a fundamental aspect of our understanding of the microscopic world. It plays a crucial role in various areas, including atomic physics, particle physics, and quantum information science.