At the beginning of a quantum computational process we generally want to start in a perfectly known initial state, and evolve from there. This cannot be done perfectly, for fundamental reasons, but I strongly suspect there has to be a practical limit below which you are in a garbage-in-garbage-out situation.
My full question is not on this input fidelity threshold per se (although feel free to provide that too), but rather on the factors to consider and minimum set(s) of requirements one needs to prepare a good-enough initial state (maybe Di-Vincenzo-list style, but preferrably with some example numbers). Presumably the perfect answer has different sections, for example depending on whether one employs thermal initialization or algorithmic cooling.
For a little more context, this question is related with certain aspects of previous ones:
- Are there measuring standards (and units) for the identification of qubits? (what could this kind of prospective standards say about initialization in different platforms?)
- Are true Projective Measurements possible experimentally? (perfect projective measurements plus sufficiently coherent operations -including quantum error correction- would make good-enough initialization, but how do we deal with imperfect projective measurements?)
- Is it true that observing a quantum state will end the superposition of states, and how not to observe? ("How can i be sure my input was put in without looking?")