could someone please explain what Geometric/berry phase is I've had a look and there seems to be several ways to interpret the physics. My understanding is that it occurs when your quantum state traces out a closed path in some parameter space, which is some how related to degeneracies in a hamiltonian. What is this parameter space if we are thinking of an electrons spin say? Is it always the same or does it depend specifically on the hamiltonian

thanks in advance

ohhh and if anyone has any good elementary references I would be very interested

Marks