Expectation value of X and Y component of angular momentum

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SUMMARY

The expectation values of the X and Y components of angular momentum, denoted as and , are both zero for the state |j,m>. The calculations utilize the definitions of Jx and Jy, specifically Jx = 1/2(J+ + J-) and Jy = 1/2i(J+ - J-). The solution involves evaluating the matrix elements and , leading to the conclusion that these expectation values vanish due to the properties of the angular momentum operators and the orthogonality of the states.

PREREQUISITES
  • Understanding of angular momentum in quantum mechanics
  • Familiarity with the operators J+, J-, Jx, and Jy
  • Knowledge of quantum state notation |j,m>
  • Basic concepts of matrix elements and orthogonality in quantum states
NEXT STEPS
  • Study the properties of angular momentum operators in quantum mechanics
  • Learn about the implications of the orthogonality condition =δ_{m,n}
  • Explore the role of raising and lowering operators in quantum states
  • Investigate the significance of expectation values in quantum mechanics
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Students and researchers in quantum mechanics, particularly those focusing on angular momentum and its applications in quantum systems.

xinoki
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Homework Statement


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<Jx>=<Jy>=0

Homework Equations



Jx=1/2(J++J-)
Jy=1/2(J+-J-)

The Attempt at a Solution



<jm l Jx l jm> = < jm l 1/2 J+ l jm> + < jm l j- l jm >
= < jm l h/2 sqrt [(j-m)(j+m+1)] + h/2sqrt[(j+m)(j+m+1) l jm >

i am not sure how to apply the next step
 
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Note that |j,m> is NOT an eigenstate of either J+ or J-. In fact, J+|j,m>=k|j,m+1>, etc.

Additionally note that &lt;j,m|j,n&gt;=\delta_{m,n}
 

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