Shell-model project

For our project, we will only consider the pairing model. A simple space is the \( (1/2)^2 \) space with four single-particle states

Index \( n \) \( l \) \( s \) \( m_s \)
1 0 0 1/2 -1/2
2 0 0 1/2 1/2
3 1 0 1/2 -1/2
4 1 0 1/2 1/2

For \( N=2 \) there are 4 states with \( M=0 \); show this by hand and confirm your code reproduces it.