Pauli spin matrices and Eigen spinors

In summary: This means that the spin matrices have the same properties as the angular momentum matrices, such as being Hermitian and having integer or half-integer eigenvalues.In summary, the conversation discusses the formulation and understanding of spin 1/2 and its matrices in quantum mechanics. It is noted that there are more than just two states of spin, and an arbitrary state is a linear combination of the up and down states. The spin matrices are defined using the same commutation relations as the angular momentum matrices, giving them similar properties.
  • #1
Rahulrj
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So I have been studying the case of spin 1/2 and I have understood how the formulations work through to find the spin matrices. However I do not get an intuitive understanding of what they mean and why they are formulated the way they are. I follow Griffith's book and in it as he begins to solve the case for spin 1/2, he writes a general state for it which he calls a spinor and writes this
##[a\,b]^T =aX_++bX_{-}##
My first doubt is what does this general state mean? Isn't there only two states of spin, spin up and spin down?
and to find the matrices of ##S^2## and ##S_z## he uses their eigenvector equation to find that but why is the same method not employed for finding the matrices for ##S_x## ##S_y## ? He gets their respective matrices using a sum of raising and lowering operators Also he ends up with an eigen spinor with a different value. So am pretty much confused with how they came to be.
 
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  • #2
There are not only two states of spin. The up state and the down state together form just one possible set of basis vectors. An arbitrary state is a linear sum or superposition of the basis vectors.

Spin is defined analogously to angular momentum http://farside.ph.utexas.edu/teaching/qmech/Quantum/node87.html
 
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1. What are Pauli spin matrices?

Pauli spin matrices are a set of three 2x2 matrices used in quantum mechanics to describe the spin of a particle. They were first introduced by Wolfgang Pauli in 1927 and are denoted by the symbols σx, σy, and σz. They are used to represent the spin angular momentum and its components in a quantum system.

2. What are Eigen spinors?

Eigen spinors, also known as eigenvectors, are mathematical vectors that represent the possible spin states of a particle. They are the solutions to the Schrödinger equation for a spin-1/2 particle and correspond to the spin-up and spin-down states of the particle. Eigen spinors are used to describe the probability of finding a particle in a particular spin state.

3. How are Pauli spin matrices and Eigen spinors related?

Pauli spin matrices are used to represent the spin angular momentum of a particle, while Eigen spinors represent the possible spin states of a particle. The Pauli spin matrices are used to calculate the eigenvalues and eigenvectors of the spin operator, which correspond to the possible spin states represented by Eigen spinors.

4. What is the significance of Pauli spin matrices and Eigen spinors in quantum mechanics?

Pauli spin matrices and Eigen spinors are essential tools in quantum mechanics for describing the spin behavior of particles. They are used to calculate the spin expectation values, which can then be used to determine the probability of finding a particle in a particular spin state. These concepts are crucial in understanding the behavior of subatomic particles and their interactions.

5. How are Pauli spin matrices and Eigen spinors used in real-world applications?

Pauli spin matrices and Eigen spinors are used in various real-world applications, such as in the development of quantum computers and in nuclear and particle physics experiments. They also have applications in materials science, such as in studying the magnetic properties of materials. Additionally, they are used in medical imaging techniques, such as magnetic resonance imaging (MRI), which rely on the spin behavior of particles.

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