Quantum Homework Question: Simplifying Xjk using A|k> and A+|k>

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SUMMARY

The discussion focuses on the simplification of the operator Xjk using the annihilation operator A|k> and the creation operator A+|k>. The user successfully derived the expression Xjk = L(root k delta j, k-1 + root (k+1) delta j, k+1) but encountered an issue where the matrix entries appear to be consistently larger by 1. This discrepancy suggests a potential error in the application of the Kronecker delta or the eigenstate definitions.

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Homework Statement



Please see attached question


Homework Equations





The Attempt at a Solution



So i tried to work out Xjk by pre and post multiplying by energy eigenstates <j| and |k>

Then i simplified the expression using A|k> = root k |k-1> and A+ |k> = root (k+1) |k+1>

giving a final answer of Xjk = L(root k delta j, k-1 + root (k+1) delta j, k+1)

where delta is the kronocker delta. My problem is that all of the entries in my matrix seem to be too big by 1.

So for X_21 i get root 2 instead of root 1 etc..

what's gone wrong?

Thanks
 

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any ideas? is my notation clear?
 

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