I don't know very much the NISQ algorithms, but the ones that I know are based on kind of "Hybrid" calculation between a quantum computer and a classical computer.
Indeed, for instance in QAOA, we can try to find the fundamental of some Hamiltonian. To do this, we run a circuit with a given set of gates. We measure the qubit and "feed" it to some classical processing that either say "fundamental may have been found: stop", or "make more iterations". When "more iterations" occurs the circuit is changed according to a classical algorithm and the quantum algorithm is run again. And so on until we believe we found the solution (my summary is probably a little bit short/exagerated as I don't have in full memory the details but from what I remember it is something roughly like this)
In this algorithm there are two important features:
- There is a classical processing around that is used in parallel of the quantum which goal is to "update" the quantum circuit.
- We basically cannot know when the algorithm will stop "theoretically". It is not like in fault tolerant quantum computing where an algorithm has a fixed Depth so that we can deduce when it will stop.
I wanted to know if all (seriously considered) NISQ algorithms are based on those two elements: circuit updated from classical processing AND you don't know "in advance" when the algorithm will stop ?
From the example I read I think this is true but I don't know enough to be sure.