Hi, I think I’m still having the issue described here even though I’m using the latest ITensor. Here is an example of it using the function op_mpo defined in this discourse, where I apply a particle hole transform to a maximally mixed state (which should leave it invariant).
s = siteinds(“Fermion”,2;conserve_qns=true)
###Creating particle hole transform for site 1
cdag = op_mpo(s,“Cdag”,1)
c = op_mpo(s,“C”,1)
PH = cdag+c
##both sites are in the identity (maximally mixed state)
ρ = op_mpo(s, “Id”, 1)
ρ = ρ/tr(ρ)
apply(PH,ρ)
This code gives the error attempt to access 0-element Vector{Pair{QN, Int64}} at index [1], but without quantum numbers it works.