On the bottom half of page 249 Cohen-Tannoudji it talks about selection rules in terms of off diagonal elements of the matrix generated by ##\langle \phi _{ n^{ \prime },\tau ^{ \prime } } \mid \hat { B } \mid \phi _{ n,\tau } \rangle##. I thought all off diagonal matrix elements would be zero due to the ##\delta_{n^{\prime},n}## nature of these state vectors? Is this because it is not just a double sum with a single good quantum number? I am confused. Could you shed some light?(adsbygoogle = window.adsbygoogle || []).push({});

Thanks,

KQ6UP

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# Trying to understand Selection Rules in Cohen-Tannoudji

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