quantumlib
Allow users to compute expectation values of non-Hermitian PauliStrings/PauliSums?
From a comment in that PR:
Making it just Hermitian make sense when thinking of this as "expectation value of an observable in quantum theory". For non-Hermitian operators, sometimes you can think of them as "observables" with complex eignevalues. But sometimes you end up with non-Hermitian operators that don't a complete set of eigenvectors than span the space, so then it is really hard to interpret this as an observable.
That said, it definitely makes sense to define <x|A|x> for a non-hermitian operator. My suggestion would be to allow this via an explicit parameter. i.e. normally it requires Hermitian and throws an error that says if you want to calculate for a non-hermitian operator, set the parameter appropriate.
Closing due to age (6+ years since first opened) and prioritization. If this is in error, someone please feel free to reopen this.
