What is the purpose of introducing the spin state along H

[Pring]

The more detail you can see the attachment. I don't understand why Rabi translate the state along z axial to H axial as shown the equations (8).

 

[DrClaude]

The choice of quantization axis is purely arbitrary, and calculations are much simpler when the quantization axis is chosen parallel to the field axis. That way, you remove the coupling of different $m$ states due to the field.

 

[Pring]

The choice of quantization axis is purely arbitrary, and calculations are much simpler when the quantization axis is chosen parallel to the field axis. That way, you remove the coupling of different $m$ states due to the field.

Thank you!