Hi Miles,

I was trying to reproduce the calculation of von Neumann entanglement entropy (EE) as shown in Fig. 2 of this paper

https://arxiv.org/abs/1005.2123

Here, @@J_\text{leg} = \cos(\theta)@@, @@J_\text{rung} = \sin(\theta)@@.

I label sites of one leg from 1 to L and sites of another leg from L+1 to 2Nx.

When calculating the EE, I bipartite the ladder at site L

It looks that my code works pretty well (as attached below), except when theta is closed to pi/2.

In this case, we expect that the EE should reach its maximal value. However, from my simulation, I always get a zero EE for theta is closed to Pi/2. I am wondering is there any mistake in my code?

Thanks!

Jeffrey

Please found my code here