QITE Inconsistencies about qforte HOT 3 OPEN

I'm going to be taking this issue as I read over some of Minnich's papers.

from qforte.

The tale is more complicated than I first thought. They used different approximations in their quantum simulator compared to their noiseless simulator. The algorithm they used on their noiseless system involves non-Trotterized exponentials.

I'm still not sure the QForte implementation matches the original implementation. The basic structure of a single QITE step is to loop over all terms in the Hamiltonian, compute the step for each, and update the wavefunction gate for each. In the QForte loop, we have a "step-merged" version, where we use the entire Hamiltonian, Trotterizing when necessary.

@nstair, does this sound right to you? If we're agreed about the theory, I can implement the non-step-merged version, keeping the step-merged version.

from qforte.

@JonathonMisiewicz you are correct. The current implementation in QForte is closer to the step-merged version. You are welcome to implement the non-step-merged version, but it becomes challenging to rationalize 'inexact QITE' for non k-local hamiltonians.

from qforte.