Local conservation laws in spin-1/2 XY chains with open boundary conditions

Understand

We revisit the conserved quantities of the spin-1/2 XY model with open boundary conditions.

• In the absence of a transverse field, we find new families of local charges and show that half of the seeming conservation laws are conserved only if the number of sites is odd.
• In even chains the set of noninteracting charges is abelian, like in the periodic case when the number of sites is odd.
• In odd chains the set is doubled and becomes non-abelian, like in even periodic chains.