- #1
LagrangeEuler
- 717
- 20
Homework Statement
How to calculate?
## \sum _{i,j} \langle 0|\prod_n \hat{C}_n \hat{C}^+_i\hat{C}_j \prod_n \hat{C}^+_n|0 \rangle ##
Homework Equations
##\hat{C}^+, \hat{C}## are fermionic operators.
##\{\hat{C}_i,\hat{C}^+_j\}=\delta_{i,j}##
The Attempt at a Solution
I have a question. What is ##|0 \rangle##? Is that maybe ##|0 0\rangle##?