1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Problem from Quantum Optics

  1. Jul 25, 2016 #1
    1. The problem statement, all variables and given/known data
    What is the Expectation value of

    $$\sum_{l=0}^{n} \bra{n} (a\dagger)^l(a)^l\ket{n}$$

    where $$a\dagger$$ and $$a$$ are lowering operators
    2. Relevant equations
    $$a\dagger\ket{n}=\sqrt{n+1}\ket{n}$$
    $$a\ket{n}=\sqrt{n}\ket{n}$$
    3. The attempt at a solution
    I get the solution as $$\sum_{l=0}^{n} (n)!(n+1)!$$
    But the correct answer is $$\sum_{l=0}^{n} \frac{n!}{(n-l)!}$$
     
  2. jcsd
  3. Jul 25, 2016 #2
    Sorry I got the answer! please delete this thread
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Problem from Quantum Optics
  1. Optics Problems (Replies: 2)

  2. Optics Problems (Replies: 1)

Loading...