Relabeling spin or angular momentum operators

In summary, the concept of spin or angular momentum in this conversation is based on eigenstates of the operator measuring angular momentum along a specific axis. This can be done in any direction, such as Ly or Lx, without changing the equations. The choice of coordinate axes is a matter of convenience and does not affect the physics. This can be verified using Pauli matrices.
  • #1
aaaa202
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Spin or angular momentum in my book is formulated in the basis of eigenstates of the operator that measures the angular momentum along the z-axis. But in principle I guess this could just as well have been done in the basis of eigenstates of Ly or Lx. Will that change anything in the equations? For example for spin where all vectors and matrices are written in basis of the eigenstates of Sz.
 
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  • #2
aaaa202 said:
Spin or angular momentum in my book is formulated in the basis of eigenstates of the operator that measures the angular momentum along the z-axis. But in principle I guess this could just as well have been done in the basis of eigenstates of Ly or Lx. Will that change anything in the equations? For example for spin where all vectors and matrices are written in basis of the eigenstates of Sz.

The physics is the same in all directions. First we pick a direction that we'll measure the spin along, then we choose a set of coordinate axes. For convenience and because it simplifies the calculation, then we choose the axes so that one of them points along the chosen direction, and then by convention we label that axis z.
 
  • #3
You can cyclically permute the directions. x->y, y->z, z->x (or reverse) without changing anything. A simple exercise is to verify that the math all works out using Pauli matrices.
 

What is relabeling spin or angular momentum operators?

Relabeling spin or angular momentum operators is a process in quantum mechanics where the basis states of a system are changed by relabeling them with different quantum numbers. This is done to simplify calculations and better describe the system.

Why is relabeling spin or angular momentum operators important?

Relabeling spin or angular momentum operators is important because it allows for a more convenient and concise description of the quantum system. It also helps to better understand the properties and behavior of the system.

How is relabeling spin or angular momentum operators done?

Relabeling spin or angular momentum operators is done by applying mathematical transformations to the original basis states of the system. These transformations can involve changing the labels of the basis states, reordering them, or combining them in different ways.

What are some examples of relabeling spin or angular momentum operators?

One example of relabeling spin or angular momentum operators is the transformation from Cartesian coordinates to spherical coordinates. This involves relabeling the basis states of a system from (x, y, z) to (r, θ, φ). Another example is the transformation from the spin-up and spin-down basis states to the +z and -z basis states.

What are the benefits of relabeling spin or angular momentum operators?

Relabeling spin or angular momentum operators can lead to a simpler and more intuitive description of the quantum system. It can also make calculations and predictions easier and more accurate. Additionally, relabeling can reveal new symmetries and relationships within the system.

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